A tragic auto accident outside Austin, Texas, has taken the life of John F. Gregory, creator of the Gregory-Maksutov telescope design. He was 82. Preliminary details are in this news account. His wife, Carolyn, remains in critical condition following the November 14, 2009, crash.

For amateur telescope makers (or ATMs), Gregory charted a new course with his seminal article, "A Cassegrainian-Maksutov Telescope Design for the Amateur," in Sky & Telescope for March 1957. No longer was an ever-larger Newtonian reflector the only thing on glass-pushers' wish lists. Gregory showed how to make a far more sophisticated telescope, not unlike the high-end Questar catadioptric telescope that began to be a commercial rage in the 1950s. John didn't just provide the curves and specs for an experienced mirror-maker to work to; he presented the shop techniques and exacting tests needed for a successful completion.

Soon after that article appeared, other key players grabbed the baton. Bob Cox, conductor of S&T's Gleanings for ATMs department, published many more articles by Gregory and other Maksutov enthusiasts. This soon led to the classic 39-page pamphlet, Gleanings Bulletin C. And Scottish-born instrument maker Allan Mackintosh launched the Maksutov Club, for which he began issuing monthly circulars to a generation of advanced ATMs.

Gregory, who was then living in Stamford, Connecticut, went on to design a 22-inch f/3.7 Maksutov photovisual telescope. This instrument was completed in 1965 for the Stamford Museum and Nature Center and ranks as the largest Maksutov in the U.S.A. He was then employed as an optical engineer at Perkin-Elmer, but later he moved to Dripping Springs, Texas, to start his own consulting firm, John Gregory Optics. In 1980 he donated an 8.2-inch f/16 Maksutov-Cassegrain that he'd made to his alma mater, Case Western Reserve University in Cleveland, Ohio. He named it the Nassau Memorial Telescope after his former teacher there, noted spectroscopist and Milky Way expert J. J. Nassau.

Meanwhile, Gregory continued to share his expertise, often turning up at annual ATM gatherings such as Stellafane in Vermont and the Riverside Telescope Makers Conference in California. He was equally at home crunching numbers, circumambulating a pitch lap, or operating a machine-shop lathe. Nowhere does this multifaceted mastery come across more clearly than in his last major S&T article, "The Quest for the Perfect Refractor" (June 1987, pages 662–667).

Gregory's longtime friend and associate Mike Jones is collecting tributes and recollections. For his enthusiastic leadership in telescope making, Mike notes, "John was one of the last of the great ones, right up there with Russell Porter, Al Ingalls, James G. Baker, and Bob Cox."

Back in the 1960s and early '70s, planetary exploration was a purely ballistic exercise: launch a spacecraft to Earth's escape velocity, point it in the right direction, and some months later it would arrive wherever — be it Venus, Mars, or Jupiter.

These days it's usually a lot more complicated. Take the case of the Rosetta. Launched in 2004 by the European Space Agency, this craft is en route to Comet 67P/Churyumov-Gerasimenko — but it won't arrive until May 2014. The spacecraft is taking the scenic route through the inner solar system — making three flybys of Earth and one of Mars to build up the speed needed to catch up to the comet.

Rosetta picked up another I've-been-there postcard on November 13th, when it swept past Earth for the last time. It glided by at 7:46 Universal Time, passing over Indonesia about 1,540 miles (2,480 km) up. It's now logged just about two-thirds of the 4.4 billion miles (7.1 billion km) it'll log by the time it reaches. It'd have been shorter going straight to Pluto!

Unlike the Rosetta's September 2008 encounter with asteroid 2867 Steins, which served as target practice for the 11 instruments aboard, this time the European comet-chaser did only a little sightseeing. Even so, Friday's flyby gave the craft a swift kick, boosting its velocity by about 2.2 miles (3.6 km) per second that will drive it even farther outward.

Rosetta plans a swing past the minor planet 21 Lutetia in July 2010. A year later, ESA controllers will put Rosetta in electronic hibernation until spring 2014, a few months before it sidles up alongside Churyumov-Gerasimenko and drops an instrumented lander onto its icy surface.

Besides the view posted above, you'll find other nice views from the flyby and an animation here.

With all the hubbub over LCROSS's confirmation of water on the Moon, it's easy to lose sight of NASA's primary mission there, the Lunar Reconnaissance Orbiter. But so far, LRO's observations have been "breathtaking," says project scientist Richard Vondrak.

Exhibit A is this view of the Apollo 11 landing site acquired on October 1st (but not released until November 9th) by the spacecraft's high-resolution stereo camera, LROC. It reveals details at the Space Age's most hallowed ground down to about 2 feet (53 cm).

Spend a little time perusing the image at right — or go moonwalking yourself by downloading a larger version or even the original image. The LROC team released a lower-resolution view of the landing site a couple of months ago, but now the spacecraft is in its final mapping orbit, a scant 30 miles (50 km) above the lunar surface.

You can easily see the squarish descent stage of the lunar module Eagle, which looks washed out because of contrast enhancement — look closer, and you'll make out its footpads too. Dark trails are the paths made by astronauts Neil Armstrong and Buzz Aldrin as they walked near Eagle and around the Early Apollo Science Experiments Package (EASEP).

A few weeks ago, the LROC team released a video tour of the Apollo 17 landing site — amazing stuff! I guess those who still believe that NASA faked the lunar landings would argue that these pictures have been doctored.

It's hard to believe, but just a year ago, five spacecraft were orbiting the Moon — none of them launched by NASA. India and China had one each (Chandrayaan 1 and Chang'e 1, respectively), while Japan's Kaguya and two small escorts, named Okina and Ouna, were mapping the Moon inside and out.

Waiting in the wings was LRO, which began circling the Moon last June. Designed and built at a time when the U.S. and its space agency were firmly committed to returning humans to the Moon, LRO is a recon mission in the truest sense. Its seven-instrument payload reflects NASA's desire to understand the lunar features and resources that could influence the design and placement of future lunar settlements.

For example, the spacecraft's low polar orbit should allow its cameras to record the entire globe with 100-meter resolution and up to 10% of the surface with unprecedented 0.5-meter resolution — good enough to spot hazardous boulders in likely landing sites. (In fact, the view here shows boulders from West crater, which lies out of view to the right in the Apollo11 view above.) A radar mapper and a laser altimeter are gauging the slope and roughness of the terrain. The Diviner instrument has been recording temperatures from pole to pole, and a Russian-built neutron spectrometer is finding the "sweet spots" where deposits of water ice lie buried. Finally, a cosmic-ray telescope has been assessing the hazard that space radiation poses for future explorers.

LRO's early efforts concentrated on the lunar poles, in order to pick the best target for LCROSS and the Centaur rocket that carried both craft to the Moon. But Vondrak hopes that LRO can continue clicking and scanning the lunar landscape for at least two more years. Plans call for modifying the orbit periodically to optimize coverage, ending with the spacecraft in a gravitationally stable "frozen orbit" with a low point almost directly over the Moon's south pole.

When NASA's Lunar Crater Observation and Sensing Satellite (LCROSS) and its empty Centaur rocket slammed into the inky darkness of Cabeus crater on October 9th, a worldwide audience watched for some much-anticipated lunar fireworks.

But as space spectacles go, the LCROSS impacts were a bust. No incandescent flash lit up the monitors in mission control, nor did billowing plumes of dust stream upward into the sunlight and into view of telescopes back on Earth. Astronomers sifted through flat-lined observations from Hubble, Keck, Gemini, Subaru, and other giant eyes, looking in vain for any trace of the event. The poor showing frustrated legions of backyard Moonwatchers as well.

One problem was that telescopic views of the impact sites were blocked by a high ridge along the Earth-facing rim of Cabeus. The plume had to rise at least a mile (1½ to 2 km) before it emerged into sunlight and Earth view — and by then, apparently, it had become too diffuse to see. The only positive detections from Earth involved a pulse of sodium added to the Moon's tenuous exosphere.

Nothing, however, blocked the view of the nine cameras and spectrometers aboard the LCROSS shepherd probe, which trailed the rocket by about 400 miles (600 km). In addition, the Lunar Reconnaissance Orbiter had a front-row seat as it passed horizontally just 48 miles (76 km) overhead. Those instruments detected a flash when the Centaur hit, the rising plume of hot debris that followed (recorded in the image above), and the crater left behind. In that sense the mission was a smashing success.

The rocket's impact gouged a pit about 70 to 100 feet (20 to 30 m) across, in line with expectations. A splash of debris extends another few hundred feet (80 to 100 m) or more beyond the crater rim. But LCROSS project scientist Anthony Colaprete concedes that the incandescent flash created by the Centaur's impact was only a third as bright as predicted, a dim blip that his team struggled to find amid the underexposed camera frames. (Maybe they should have consulted amateur occultation timers, who routinely record faint events on the Moon's brilliant edges.)

Success at last

Not until today, after the team had pored over the results for several weeks, was Colaprete finally able to announce that water vapor was present in the towering plume of hot dust and gas. "Multiple lines of evidence show water was present in both [the] high-angle vapor plume and the ejecta curtain created by the LCROSS Centaur impact."

An infrared spectrometer on LCROSS recorded absorption bands of water vapor at wavelengths of 1.4 and 1.85 microns (see spectrum at right). Another spectrometer registered ultraviolet emission at 309 nanometers, a telltale sign of hydroxyl (OH) radicals created when water molecules break apart in ultraviolet sunlight (see spectrum below).

So there is water on the Moon — and "we didn't find just a little bit, we found a significant amount," Colaprete said. He estimates that the part of the plume in the instrument's field of view contained about 100 kg of water vapor, or about 25 gallons if it were liquid. He would not yet give an estimate yet of what fraction of the lunar soil that amounts to; the answer to that question will depend on how much soil was kicked up and how much was outside the field of view.

By comparison, other observations — including early results from a Russian-built experiment aboard LRO, the Lunar Neutron Exploration Detector, that senses where hydrogen (in water, presumably) is concentrated in the lunar landscape — suggested that the near-surface rubble inside Cabeus might hold 1% water or more by weight.

Water's spectral fingerprints weren't the only ones found by LCROSS. Apparently the blossoming debris cloud had other interesting "flavorings" mixed in. Mission scientists are still trying to make the best fits to the observed spectrum, but candidate compounds include carbon dioxide (CO₂), carbon monoxide (CO), and even organic molecules like methane (CH₄), methanol (CH₃OH), and ethanol (C₂H₅OH). "The possibility of contamination from the Centaur was ruled out," Colaprete notes.

Geochemists had a hunch that the crash might dredge up a strange brew. They'd been tipped off back in mid-September by results from Diviner, an LRO instrument designed to map temperatures across the lunar surface. Its sensors found that the polar regions are far colder than expected, as low as 35K (–397°F) in some spots. As improbable as it is remarkable, the shadowed floors within Cabeus and its neighbors are the most frigid places so far measured anywhere in the solar system. That should make them efficient "cold traps" for volatiles of all kinds.

So a whole host of compounds could be in the mix. "It's lot more complicated than we really anticipated," Colaprete admits. "The eureka moment was seeing the OH line, but we haven't had time to enjoy it — because we're so interested in everything else that's in there."

"We're really not done yet," echoed Michael Wargo, chief lunar scientist at NASA Headquarters. He refered to the Moon's permanent polar shadowlands as "the dusty attic of the solar system," where all sorts of volatiles may have collected for the last 1 or 2 billion years, providing a unique record of solar-system events. Team members pledged to announce other results as they gain confidence in the ongoing analyses. They plan to present some additional findings at science meetings next week and in early December.

No one has heard from Phoenix for more than a year, ever since NASA's polar lander succumbed to the circuit-shattering cold of the approaching Martian winter. Yet the mission's scientists and engineers are still keeping an eye on their charge, and new views released this week show the lander partially mantled in dry-ice snow.

Last July and again in August, the HiRISE camera aboard Mars Reconnaissance Orbiter returned its gaze to the bleak plain called Scandia Colles, at a latitude of 68° north, where Phoenix touched down on May 25, 2008. The orbital views show the lander in dim light as northern winter neared its end. The view here gives the impression of frosty patches atop ice-free ground, but that's an artifact of contrast enhancement. In fact, the entire scene is covered with frozen carbon dioxide.

We'll probably never know how just how much CO₂ snow accumulated atop the lander by September, when the coating was likely thickest, because the orbiter has had problems of its own. After four self-induced shutdowns earlier this year, MRO remains in electronic hibernation while ground controllers try to cure its problems. That means HiRISE has been unavailable to monitor conditions at Phoenix's landing site as sunlight returns and the blanket of dry ice slowly vaporizes.

Thomas Prettyman (Planetary Science Institute) estimates that, at its peak, the pile of CO₂ in the lander's vicinity would total about 30 grams per square centimeter. That's enough to make a dense slab of dry ice at least 7½ inches (19 cm) deep, or a much thicker layer if it were the fluffy stuff. "This would be similar to having a foot of solid water ice on top of your car here on Earth," Prettyman explains. "It's probably not a good idea to leave your lander out in the snow."

With temps having plunged plunged to -240°F (-150°C), engineers give the unheated Phoenix little chance to survive. The craft's fragile solar-cell arrays, not designed to support much weight, have likely cracked and fallen off from the weight of all that dry ice.

Still, the team will try to reestablish contact in about a month, when the seasonal situation will be much like that when Phoenix landed. Ground stations will send a wake-up call to the spacecraft as the Mars Odyssey orbiter is overhead and listening for a response. "The solar-cell panels must revive the battery and bring the computer system up to working order," explains project scientist Peter Smith (University of Arizona). The communication system must also revive, and the lander must be awake while Odyssey is overhead.

"It's a lot to expect," Smith admits, "but we will try."

Launched last March, NASA's Kepler spacecraft is designed to find Earth-size planets around other stars. The observing strategy is simple: use Kepler's big telescopic eye to stare at a patch of sky covering 105 square degrees near the Cygnus-Lyra border.

Any time a planet passes in front of one of the estimated 100,000 stars within the target area, the spacecraft records the temporary dip in the star's light. This gives the mission's scientists enough information to deduce the size of both the planet and its orbit.

In August, for example, chief scientist William Borucki and other team members showed Kepler's promise by recording the passage of a known exoplanet, dubbed HAT-P-7b, in front of its host star. The spacecraft was working just as planned.

But last week Borucki told a NASA advisory panel that there's a problem with some of the craft's light-sensing detectors. To cover this much sky, Kepler uses an array of 42 detectors, each divided in half for ease of data transfer. It turns out that three of those 84 detector channels are noisy, and the stars in these areas appear to flicker — not a good thing if you're trying to detect minuscule changes caused by transiting planets.

Apparently the Kepler team knew about the noisy channels prior to launch, but the cure (disassembling the flight-ready craft to replace the bad electronics) was deemed worse than the disease. Instead, for now output from the three channels will simply be ignored, and a computer program should be ready by 2011 to filter out the flickering.

In the meantime, since the other 81 detector channels are unaffected, the planet hunting goes on. Once one of the target stars winks and a candidate world is identified, the team will record at least two more transits before feeling secure about the discovery. For a planet in an Earth-size orbit around a Sunlike star, this confirmation might take three years — by which time the noise-canceling software should be in place.

By contrast, the "habitable zones" for lower-mass dwarf stars lie closer in, so the orbits of planets in those zones will be smaller and their orbital periods shorter. Should one of these candidate solar systems fall in one of the noisy fields, its discovery might be delayed for up to a year, according to Borucki.

There's a countdown clock in the control center at the Johns Hopkins University's Applied Physics Laboratory. It tells scientists and engineers the time remaining until their Messenger spacecraft enters orbit around the planet Mercury on March 18, 2011.

Auspiciously, today the clock rolled through "T-500 days." Maybe that milestone was the reason that Sean Solomon, the mission's principal investigator, chose to hold a press briefing today about results from the spacecraft's third and final flyby of the innermost planet. (I wouldn't put it past him!)

The September 29th visit provided the final gravitational tweak to the craft's trajectory, and in that overarching sense things went perfectly. Solomon notes that this was the most accurate flyby of the six executed by Messenger since its launch in August 2004. But he also conceded that a glitch in the on-board electronics occurred just as the craft closed to within 142 miles (228 km) of Mercury's night side. Any observations planned during the second half of the flyby — and that's a long list — were lost. (More on the significance of that miscue in a moment.)

Still, the science team has plenty to chew on, especially regarding the exosphere that envelops the planet. It's not really an atmosphere in the usual sense, because the ultrathin gas escapes readily to space and thus must be constantly replenished. Nor is the composition anything like what we're used to. There's sodium and potassium, which had been detected by observers on Earth, along with calcium and magnesium. These atoms are removed from the surface either by the intense sunlight, space radiation, or micrometeoritic bombardment. As investigator Ron Vervack Jr. (APL) succinctly summarized, "Something smacks into the surface and knocks stuff off."

Once "airborne," these atoms are either swept behind the planet by the sunlight's radiation pressure or become ionized by it. Vervack reported that the amount of exospheric sodium was only 5% to 10% that measured during the craft's second flyby, a falloff that had been expected due to Mercury's orbital location.

More puzzling is the interplay of the calcium and magnesium. "We are now seeing conclusively that the magnesium is behaving differently than the calcium," Vervack told me. They should behave similarly from a chemical standpoint and require a sizable kick to be launched from the surface — so why are their distribution in Mercury's exosphere so different? "High-energy processes should be doing the same thing to both, but they clearly are not," he continues. "We don't have an answer for why yet."

Vervack isn't the only Messenger investigator left scratching his head by Messenger's flybys. There's a growing mystery about what, exactly, is in the planet's surface rocks. Mercury has long been dubbed the Iron Planet, because its metallic core fills nearly half of Mercury's innards and accounts for at least 60% of its mass. Yet over the years ground-based spectroscopists have consistently seen the signatures of iron-poor silicates across the Mercurian landscape. That, in itself, is perplexing, given how much of the planet seems to be covered with volcanic flows.

David J. Lawrence (APL) stirred the geochemical pot by announcing that there's likely a lot of iron, as well as titanium, on the planet's surface. "It's an exciting result," he says, "not one we expected."

The evidence comes from Messenger's neutron spectrometer, which has found a dearth of low-energy neutrons coming from Mercury. These neutrons arise when cosmic rays slam into the surface and smash atoms within the rocks to smithereens. Iron and titanium soak up the just-formed neutrons like little atomic sponges, so the low counts are telling us that the abundance of iron must be high — comparable to what's found in mare basalts on the Moon's near side (which is up to 14% by weight).

Lawrence explains that while iron would ordinarily combine readily to form rock-forming silicates in a cooling magma, under certain circumstances iron and titanium oxides might condense out first, leaving the silicates with little iron to incorporate. This would explain the iron-poor silicates inferred from telescopic observations, while still allowing the surface rocks to contain abundant iron.

The compositional maps that Messenger compiles once in orbit should eventually sort this all out, but for now the conundrum looms large. In the minds of the mission's geochemists, Question Number One is where all the iron came from that dominates Mercury's interior. The overall density is too high for this planet simply to have assembled from the mix of compounds present near the Sun when the solar system formed.

So one of three things happened: (1) somehow Mercury came together with a paucity of lower-density silicates, the kind found abundantly in Earth's crust; (2) it endured a period of extreme heating from the young Sun, which caused many elements simply to boil away; or (3) something really big collided with Mercury and stripped away the lion's share of its crust and mantle.

If (1) is correct, then the surface will be covered with a mixture of common minerals. By contrast, the evaporation model (2) would have left the planet depleted in "volatile" elements like potassium and sodium — but then what's the source of these atoms in the exosphere? If an impact is the cause, then the surface rocks should be enriched in iron.

So is Door Number 3 the correct one? Maybe, but not necessarily. The earlier flybys revealed that volcanic plains cover much of Mercury. So perhaps those dark iron-infused flows mask a crust with a markedly different composition.

No doubt the science team wishes the electronics hadn't gone flaky during the flyby's crucial moments — among the lost data were numerous targeted observations pairing the craft's cameras with a spectrograph that samples visible and near-infrared light at wavelengths diagnostic of iron and titanium-bearing silicate materials.

All was not lost, of course, since Messenger will have a chance to recoup those lost observations — and add thousands more — once it reaches Mercury for good … just 500 days from now.

It would be fair to say that the crashy culmination of NASA's LCROSS mission on October 9th was a technical success but a public-relations fizzle.

On the plus side, the engineering team for LCROSS (short for Lunar Crater Observation and Sensing Satellite) delivered as promised, deftly driving a spent 2½-ton Centaur rocket into a target zone near the Moon's south pole only 2 miles (3½ km) across. Four minutes later, after flying through the debris cloud raised by the rocket's crash, an instrument-packed 600-kg "shepherding spacecraft" augered in not far away.

But the team's hope of finding abundant water buried in the permanently shadowed floor of Cabeus, the 61-mile-wide target crater, has yet to pan out. Water molecules have strong spectral signatures in the near-infrared, and even one part water ice in 200 parts lunar dust should have been easy to spot.

So far, the LCROSS team has been mum on what's been found by the shepherd craft's nine instruments, apart from a heavily processed composite image showing a faint puff where the Centaur crashed.

Tony Colaprete, LCROSS's chief scientist, says that the rocket's impact created a pit about 92 feet (28 meters) across, close to expectations. And the debris plume from the crash attained roughly the size and height expected, though he concedes that it was only about a tenth as massive as he'd hoped (nowhere near the 350 tons touted in some predictions).

We may never learn the reasons for the paltry particle production, though right now Brown University impact specialists Peter Schultz and Brendan Hermalyn are saying, "Told ya so!" Their modeling, based on small-scale hypervelocity collisions at NASA's Ames Research Center, suggest that a low yield should have been expected — both because the empty Centaur collapsed into itself as it hit and because the spray of debris went mostly "out" instead of "up."

It's also possible that the Centaur pancaked into the crater's floor. "It was definitely rotating or tumbling," notes observer Marc Buie, who tracked the rocket's final hours with the 2.4-m telescope at Magdalena Ridge Observatory in New Mexico.

All this speculation is intriguing — but "Where's the beef?" you might ask. Colaprete assures me that all the instruments in the shepherding spacecraft got great results, and that the delay in revealing the compositional analyses stems from having lots of spectral signatures to sort through and categorize. Colaprete says some of these findings will be made public in a couple of weeks. (Don't be surprised if he announces that one of the spectrometers did, indeed, detect water in the plume.)

For now, let me tantalize you with a preliminary result from the Lunar Reconnaissance Orbiter, which viewed the Centaur's demise from nearly overhead and just 48 miles (76 km) up. An instrument dubbed the Lyman-Alpha Mapping Project (LAMP) probed the ultraviolet spectrum of the impact plume after it had risen high enough to be projected against black space above the lunar limb.

"We definitely saw something," notes LAMP scientist Randy Gladstone (Southwest Research Institute). But that "something" wasn't water. Nor was it oxygen or hydrogen atoms, both of which have strong ultraviolet emissions. There's some hint of hydrogen molecules (H₂) — and though water is one source of hydrogen, it could also have come from silicate minerals, solar-wind gas trapped in the lunar soil, or (most likely) residual fuel in the Centaur's tanks.

LAMP's strongest and most intriguing observation came at the ultraviolet wavelength of 184-185 nanometers. Gladstone says the only known elements able to create that line are iron, perhaps magnesium … and mercury. "Both mercury and iron still look like the best bets for explaining the plume emission we see with LAMP," Gladstone reiterates, though the spectral match is still tentative and more data-crunching is in progress.

Liquid mercury on the Moon? Really? Gladstone directed me to an obscure, decade-old research paper titled "Don't Drink the Water" written by George W. Reed Jr. (Argonne National Laboratory). Reed describes how mercury was found in lunar regolith returned by the crews of Apollos 12, 15, 16, and 17, and other work suggests it might be present in the Moon's wispy-thin exosphere.

No matter what its source, Reed concludes, some of this mercury must end up as deposits in the ultracold interiors of permanently shadowed lunar craters. Moreover, the Centaur slam may not have created the big splash everyone wanted, but it only needed to heat the target area to about 200°F to release any mercury trapped in the dark dirt. And thermal imaging from the Diviner instrument aboard LRO argues that the impact site got that hot and then some.

This is all starting to make sense. Back in mid-September, UCLA scientist David Paige announced, based on Diviner's thermal mapping, that the lunar polar regions are far colder than expected, down near 35 kelvins (-397°F). This means the shadowed floors within Cabeus and its neighbors are the most frigid places known in the entire solar system. More to the point, Paige notes, "The temperatures in these super-cold regions are definitely low enough to cold-trap water ice, as well as other more volatile compounds for extended periods."

So is lunar water safe to drink? Future astronaut crews had better bring along some serious water-purification gear if they intend to live off what they scavenge from the lunar poles.

Maybe you saw it in today's news: astronomers have broken the record for the farthest thing ever seen. It's the gamma-ray burst GRB 090423, seen to happen last April 23rd in Leo, with a redshift of about 8.1. That means its light has been travelling through expanding space for 13.1 billion years, and that the burst took place 630 million years after the Big Bang.

If that sounds familiar, it's because we reported the news last April; read it here. The journal Nature issued a press release about it today, which is why it's being treated as if it were breaking news.

The burst occurred around the end of the "Dark Ages" following the Big Bang, when the universe was lighting up with stars and quasars.

Interestingly, however, the burst turns out to have properties matching bursts occurring later. The very first stars ("Population III") are thought to have included many that were much more massive and brilliant than those that formed later, because the first ones were completely uncontaminated by the traces of heavy elements that make a star's interior less transparent. Such uncontaminated, supermassive stars might explode in their own type of gamma-ray burst — and indeed, the most ancient bursts do seem to be systematically more powerful, and perhaps of shorter average duration, than later ones.

On the other hand, wherever Population III stars started living their brief lives and dying, massive stars made of second- and later-generation material might quickly start forming and dying too.

The hunt for more record-breakers continues. Bursts out to redshift 20 or greater should be detectable with current technology.

Two research papers and a review article about GRB 090423 appear in the October 29th issue of Nature:. paper 1, paper , review article.

Nature also put out a video news release.

Posted by Alan MacRobert, October 28, 2009

Back on October 8th, something big lit up the late-morning sky (at about 3:00 Universal Time) over the island nation of Indonesia.

I first learned of this event three days later, when few details were known. A smattering of news reports described an extremely bright daytime bolide that exploded high above the town of Bone in the province of South Sulawesi. One television station showed amateur video of a tortured smoke train lingering in the sky, and unconfirmed reports suggest that a 9-year-old child died of cardiac arrest from the thunderous air show.

Since then, however, impact specialists have been quietly working behind the scenes to try to determine how much punch this cosmic interloper packed. According to a preliminary analysis released October 20th by Elizabeth Silber and Peter Brown (University of Western Ontario), the sky really was falling that day. The blast registered as extremely low-frequency atmospheric waves at 11 of the infrasound stations maintained worldwide by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO).

Silber and Brown note that the high-altitude explosion was centered at 4½°S, 120°E, but it's been challenging to gauge the kinetic-energy punch it delivered. The most likely estimate is equivalent to some 40,000 tons of TNT, about three times the energy of the nuclear bomb dropped on Hiroshima in 1945. If that value is correct, this was the most powerful meteoric blast since 1994, when a "mini-Tunguska," nearly as bright as the Sun, exploded over the tiny Pacific island of Kosrae. Brown and others estimate that events like this should occur about once per decade.

Something this obvious would not have escaped the notice of various defense satellites, because these cosmic intrusions look much like nuclear weapons exploding high in the atmosphere. (Here's a list of previous airbursts picked up by the U.S. military's "orbital assets" and made public afterward.)

It'd take a chunk of asteroid about 20 to 30 feet (5 to 10 meters) across to deliver a 40-kiloton wallop. But no one has yet claimed to have found any meteorites, according to Thomas Djamaluddin, a government scientist who's been monitoring the situation. Odds are that any surviving fragments fell into offshore waters.

At an international conference on extrasolar planets being held in Portugal, a group of European astronomers unveiled on Monday a list of 30 new exoplanets and two brown dwarfs orbiting more-or-less Sun-like stars. This brings the known exoplanet catalog to a total of 403 worlds.

The new additions were all found by the radial-velocity wobbles that they induce in their host stars, as detected by the HARPS planet-hunting spectrograph on the European Southern Observatory's 3.6-meter telescope at La Silla, Chile.

The European astronomers say that HARPS can measure a star's radial-velocity patterns with an accuracy as fine as 1 meter per second: slow walking speed. This would put HARPS at the head of the accuracy list in the hotly competitive world of exoplanet hunting. Such precision is essential for detecting relatively low-mass planets — not just "super-Jupiters," "Jupiters," and "Saturns" of other stars, but the "Neptunes" and "super-Earths" that are at the limits of current technology.

According to a press release from the European Southern Observatory about the new finds, "HARPS has facilitated the discovery of 24 of the 28 planets known with masses below 20 Earth masses. As with the previously detected super-Earths, most of the new low-mass candidates reside in multi-planet systems, with up to five planets per system."

In particular, says Stephane Udry (Geneva Observatory), the HARPS project suggests that at least 40% of solar-type stars have these smaller planets. "These low-mass planets are everywhere basically."

Limits of Technology

To extract the very slight, periodic radial-velocity changes in a star that signify an orbiting planet, astronomers have to subtract out the much larger continual changes caused by the telescope's own motion on the rotating Earth, Earth's curving motion around the Sun (at about 30,000 meters per second), and even the gravitational influences of the Moon and our solar system's other planets on Earth. All these effects are precisely known. But there may be trickier confounding factors on the distant star itself, such as surface turbulence or starspots that mimic a change in the star's radial-velocity signature as the star's rotation carries the spots around.

Nevertheless, astronomers don't think they've yet hit the fundamental limits of the radial-velocity method for finding planets. For particularly good "quiet" stars, it may be possible to reach accuracies measured in centimeters per second, and thus planets as low-mass as Earth. Such hunts could become possible as early as next year.

Selections from the Harvest

What are the new planets and their stars like? The stars, according to a preliminary list, range from spectral type F6 to M: from somewhat larger and hotter, to much cooler and dimmer than the Sun. The orbiting objects have minimum masses (not necessarily the true mass, but probably not too far off) ranging from 53 down to 0.017 Jupiters. That's from 17,000 down to 5 Earth masses. Their announced orbital periods range from 4 days to 13 years (though HARPS has only been working for five years).

Of special note, three of the planets orbit stars with a lower proportion of heavy elements than are in the Sun — with a "metallicity" of only 1/3 to 1/2 the Sun's. It's well known that the greater a star's metallicity, the more likely it is to have planets detectable. A subgroup of the European astronomers targeted low-metallicity stars in particular, and their finds confirm that planets do sometimes form in a moderately heavy-element-poor environment. Clearly more than this one factor is at work in determining whether a star will have planets, even big ones.

Several systems also show radial-velocity hints of additional objects in longer-period orbits that will require years of further tracking to confirm.

Here's the ESO press release.

Here's the Extrasolar Planets Catalog reordered so the new discoveries form the top of the list.

P.S.: Don't expect the total to stay near 400 for too long. The Kepler mission should announce a whole flotilla of transiting exoplanets in the coming months.

In case you haven't heard, there's a piece of hysteria going around (pumped up by movie marketing) that the world will end on December 21, 2012, supposedly based on astronomy and an ancient Mayan prediction.

Did the Mayans really think this? Is the astronomy for real? Do we actually have anything to worry about? The answers, not surprisingly, are "no," "no," and "of course not."

To make a long story short, December 21, 2012, really is a big flip-the-page date in the ancient Mayans' calendar. But there's no evidence that they believed the world would end then, and a fair amount of evidence to the contrary. Not that it would matter if they did. As for the planetary and galactic lineups that latter-day doom-mongers have tried to associate with that date, they're flat-out wrong.

But you probably have friends and family who are getting nervous that America will crack apart into cookie crumbs, tsunamis will sweep over the Himalayas, Earth's poles will flip, and a secret invisible planet will smack us down like a bowling pin. And they will be turning to you, the astronomy person, to ask about it.

We have the stuff you need to tell them. Noted archaeoastronomer E. C. Krupp explains all the details, and the history of this mania, in the cover story of the November 2009 issue of Sky & Telescope, now available at a newsstand near you. You probably won't find it in your supermarket, but it should be on the magazine rack in any good bookstore. And if it's sold out, you can always subscribe!

Incidentally, in that same issue, S&T editor-in-chief Robert Naeye describes some cosmic catastrophes that actually could happen — and explains why they're not likely to strike in the next millennium or two. Humanity has more pressing things to worry about.

P.S. A tidbit from Krupp's article: Boston University has a Center for Millennial Studies, and its director, historian Richard Landes, points out that throughout history, failed end-of-the-world movements have numbered in the "hundreds of thousands at least." There's never a shortage of people eager for everything to go kaput. Or at least to spin hoaxes about it.

Let me introduce you to Mel. He's a little stuffed koala that my wife and I take on our travels, and as it turns out we much prefer to take pictures of where Mel has been been than where we've been.

Last week Mel found himself in Puerto Rico, where I was covering the 41st annual meeting of the American Astronomical Society's Division for Planetary Sciences. After the meeting concluded, we headed west from San Juan to visit Arecibo Observatory.

I'd been to Arecibo before, but on this particular visit I was keen to see the big dish in action. Luckily, that evening astronomer Marina Brozović (Jet Propulsion Laboratory) planned to "ping" a small near-Earth asteroid designated 1999 AP₁₀ to try to determine its shape and surface characteristics.

These are challenging times for the observatory. In 2006, a top-level review for the National Science Foundation concluded that the facility should either find funding from non-NSF sources or be closed. Even though an National Research Council report released last month affirms that the observatory provides "unmatched precision and accuracy" in detecting asteroids or comets that could hit the Earth, as things stand now there'll be no more money to fund Arecibo's unique radar capability after fiscal year 2010. You can get more background via the Arecibo Science Advocacy Partnership (ASAP).

I'll have more to say about Arecibo's precarious future at a later date, but for now let's get back to Mel's excellent adventure. As the photos below attest, the observatory is an amazing place. In a few years it may no longer be the world's largest radio dish, but for now there's no place like it on Earth.

Mel thanks staffers Mike Nolan and Ellen Howell, who paved the way for his visit and also served as gracious hosts.

---

Update (October 17): At last, NASA has extracted a clear image of the debris plume of the Centaur rocket-body impact. The very overexposed-looking image below was taken by the plummeting shepherd probe about 15 seconds after the rocket body hit. It shows a puff of stuff (circled) some 6 to 8 kilometers wide.

The image consists of three co-added, stretched video frames. Amateur occultation timers — who are used to videoing faint events on the Moon's brilliant edges — have been lambasting the mission planners for setting the camera to give good exposures of the bright Moon, not the faint event.

A NASA feature article posted yesterday about this new development puts a positive spin on things, calling the mission "a smashing success, returning tantalizing data about the Centaur impact," and noting that "the nine LCROSS instruments successfully captured each phase of the impact sequence: the impact flash, the ejecta plume, and the creation of the Centaur crater."

"We are blown away by the data returned," says Anthony Colaprete, LCROSS principal investigator and project scientist, in the article. "The team is working hard on the analysis and the data appear to be of very high quality. . . . Within the range of model predictions we made, the ejecta brightness appears to be at the low end of our predictions and this may be a clue to the properties of the material the Centaur impacted.”

See also more LCROSS images, with detailed captions.

Update (October 11): It's clear that little if anything of LCROSS's demise was seen from anywhere on Earth, a keen disappointment to professional and amateur astronomers who'd hoped to see it.

However, the results were more positive from the Lunar Reconnaissance Orbiter, which was nearly overhead in its polar orbit and only 48 miles (76 km) from ground zero.

For example, all four of the heat-sensing infrared imaging channels on LRO's Diviner instrument picked up a pulse of warmth from the impact site after the crash. According to the Diviner team's news blog, the "hot pixels" in their scans imply that "the LCROSS impact resulted in significant local heating of the lunar surface." But this by itself doesn't seem like any huge news.

The LAMP instrument (Lyman-Alpha Mapping Project) on LRO did view the debris plume from the crash against the dark sky beyond the lunar limb. "We do see a blip in total signal beginning a few tens of seconds after the impact," comments principal investigator Alan Stern (Southwest Research Institute). "There are several lines that show up, like one we think is Al III [doubly ionized aluminum]; those are most likely due to the spacecraft and perhaps some lunar material that has vaporized." Again, hardly a big finding.

Update (October 10): So far two instruments on the Lunar Reconnaissance Orbiter (LRO) have positive detections. LAMP, an ultraviolet spectrometer, has a confirmed detection of the ejecta plume, and its team has begun analyzing that data. The Diviner instrument, which measures surface temperatures, has recorded before/after changes at the impact site.

Meanwhile, astronomers have begun to assess the imaging and spectroscopic observations made with the army of powerful telescopes that were trained on the Moon's south pole yesterday morning. The following table, compiled from responses to S&T queries and other press reports, lists the professional ground- and space-based sites involved in the LCROSS observing campaign.

Observatories Watching LCROSS
Facility	Location	Aperture	Result
AEOS	HI	3.7 m	TBD
Allen array	CA	(radio)	TBD
Apache Point	NM	3.5 m	No detection
CFHT	HI	3.6 m	No detection yet
Gemini N	HI	8.1	No detection yet
IRTF	HI	3.0 m	No detection
KASSI	Korea	1.8 m	TBD
Keck	Hi	10.0 m	No detection
Lick	CA	3.0 m	No detection
Magdalena Ridge	NM	2.4 m	No detection
MMT	AZ	6.5 m	No detection
Mount Wilson	CA	1.5 m	No detection
National Solar Obs.	AZ	1.6 m	Sodium detected
Palomar	CA	5.0 m	No detection
Subaru	HI	8.3 m	No detection yet
GeoEye 1	orbit	1.1 m	TBD
HST	orbit	2.4 m	No detection
Ikonos	orbit	0.7 m	TBD
Odin	orbit	1.1 m	No detection yet

The ejecta plume was seen by the ultraviolet spectrometer aboard NASA's Lunar Reconnaissance Orbiter circling the Moon — LCROSS's companion mission. In addition, LRO's imaging radiometer detected the warm impact crater.

At Keck Observatory in Hawaii, Diane Wooden (NASA/ Ames Research Center) used the 10-meter Keck II telescope with its Near-Infrared Echelle Spectrograph (NIRSPEC) to look for the signature of water vapor. According to a Keck press release, "Wooden and the other LCROSS astronomers are currently evaluating the spectroscopic data collected at Keck and the other Mauna Kea observatories for the water-vapor signature. The team plans to report their results early next week."

"Inconclusive" results so far from the 8-meter Gemini North telescope in Hawaii.

Nothing obviously seen by three large telescopes at Apache Point Observatory in New Mexico.

Video of the non-detection from Lick Observatory.

Update (October 9th): At a press conference 2½ hours after the impacts Monday morning, NASA's LCROSS team members were upbeat. They reported that the spacecraft and its instruments all performed "beautifully," but warned "It takes a while to comb through the data." Anthony Colaprete, the LCROSS principal investigator, said "we saw the crater" from the Centaur rocket-body impact and recorded other high-quality data, but he declined to say anything about water yet. (LCROSS was designed to detect an amount of frost in the soil as small as 1 part in 200.)

Colaprete displayed an infrared image of the tiny impact flash a few pixels across, and showed photometry of the flash in visible and near-infrared light: a tiny bump in a light curve. An IR camera also recorded the warm craterlet left by the Centaur, hardly more than a pixel (a few dozen meters) across.

No ejecta plume was clearly detected — at least, Colaprete stressed, by the time of the press conference (but see the LRO result below). He held out hope that the probe's spectroscopic data might yet show ejecta and its composition.

Jennifer Heldmann, coordinator of the observation campaign, displayed images from ground-based observatories. Nothing dramatic was apparent, but analysis of the images and spectroscopy continues. Infrared spectra from the MMT Observatory in Arizona, taken just before and after impact, seemed to look different, but no one at the press conference would comment about them any more definitely. At Kitt Peak in Arizona, observers recorded a flare of light at the orange sodium-emission wavelength.

The ground-based videos that were presented showed a lot of changeless black shadow behind Cabeus's bright foreground ridge — but that doesn't mean that nothing may yet come of them.

Reporters quizzed the team members about the non-event the smashup certainly looked like. Answered Colaprete, "Life is full of surprises" and later added, "I certainly hope we can dig something out of there that will be telling."

---

Original post (8 a.m. EDT, October 9th):
Early this morning, as planned, the Centaur rocket body for NASA's LCROSS probe slammed into a permanently shadowed crater floor near the Moon's south pole — four minutes before the smaller live probe followed behind. The probe, in its final minutes and seconds of life, flew through the dust-and-vapor plume from the first impact, took data with nine instruments, and radioed it back to Earth — just before creating a second, smaller impact of its own.

Cabeus is the big crater nearly filling this frame from the LCROSS probe as the probe closed in. The rocket body had already hit in the dark, permanent shadow filling the top of the crater.

NASA

Countless astronomers both professional and amateur were watching from Earth. The Moon was up in a dark, pre-dawn sky for western North America and Hawaii, where many of the world's largest telescopes were primed to grab spectroscopy of any vapor plume that became visible. Even in the daylit East, hopeful amateurs with good weather were out under a blue sky watching the crater Cabeus as the minutes counted down. And much larger numbers were watching on NASA TV.

Of course I was clouded out. But what drama on TV! We watched through the eye of the probe's camera as the probe approached the darkly shadowed part of Cabeus, frame by frame. Controllers struggled in the last minutes to adjust the image-taking rate, by the visible and thermal-infrared cameras, to cope with the unexpectedly large compressed image files that had to be radioed back.

"Mark; Centaur impact," called a flight director at NASA's Ames Research Center. The black shadow-patch showed nothing — though the probe was looking straight down into it. The seconds ticked off. In each frame the crater and its shadowed zone grew larger. Still nothing but darkness. The same, apparently, in the colorful thermal-infrared images. An announcement came that a thermal-infrared signal was detected. A few warm infrared pixels seemed to pop in and out of view. More blankness. Then the signal went dead — the probe had hit. The flight phase of the mission was over.

It should be days before the full results from the probe and ground-based are available, so stay tuned. NASA's LCROSS website will have further news updates as they are announced.

---

The shepherd probe (center) sails into the impact plume from the rocket body in this frame from a NASA simulation of the expected sequence of events.

NASA

Meteoroid impacts the size of the Centaur rocket strike happen on the Moon a few times a month, but unpredictably and at arbitrary places. This one was carefully planned. Water was the treasure NASA was hunting. Certain valleys and crater floors near the Moon's poles have been in permanent shadow for millions of years. The ground here remains so cold (as low as 40°C above absolute zero) that tiny, rare traces of water vapor, and perhaps other volatiles, could condense as frost and, over the ages, accumulate. Occasional comet nuclei hitting the Moon could supply the vapor. So might atoms of hydrogen in the solar wind reacting with oxygen atoms in surface rocks.

If water exists anywhere on the Moon in extractable quantities, a permanent lunar base, and eventual colonies of settlers, would be much more practical than if all supplies had to be carried from Earth. Water isn't just to drink. Its most important use might be to supply rocket fuel (by splitting it into hydrogen and oxygen using solar energy) and raw material for manufacturing processes.

---

No one knew how big a plume the impacts would make. LCROSS's two main components — its bullets — were the 2.2 ton Centaur rocket that propelled the spacecraft to the Moon, and the smaller, 0.6-ton "shepherd" probe guiding both craft to the target. Several hours before the strikes, the shepherd separated and dropped far enough behind the Centaur (about 400 miles) to fly through the plume created by the Centaur before crashing itself. Both hit at 1½ miles (2½ km) per second.

Theorists predicted that the rocket's strike should kick up 350 tons of debris and create a flash in visible light. From Earth's viewpoint, the flash site was hidden by the rim of the target crater. No one knew how visible the transient debris plumes rising above the crater wall might be during the next minute or so, but LCROSS scientists estimated that the main plume might appear about as bright as the lunar surface itself in the area and, as seen from Earth, a few arcseconds in size at its peak.

Posted by Alan MacRobert, October 9, 2009

related content: Solar system news, Spacecraft and space missions

links: + digg | + del.icio.us | + reddit | + permalink | + rss

Read comments (14)

Every so often, Earth is hit by a small chunk of asteroid that self-destructs harmlessly in its atmosphere. Fortunately, for the moment all the beefier asteroidal bodies in Earth's vicinity seem to be whizzing by harmlessly — planetary astronomers continue to tell us that no known body has a significant chance of hitting home for the foreseeable future.

The one known body that has been causing them a little late-night heartburn is 99942 Apophis. Roughly 900 feet (270 meters) across, Apophis is big and massive enough to do some real damage here, walloping us with the explosive equivalent of 5 megatons of TNT.

NASA's number-crunchers have found that it has a 1-in-45,000 chance of striking Earth on April 13, 2036. But that mildly unsettling prediction hadn't been updated since 2006, and yesterday the Minor Planet Center issued recent observations and a new orbit.

Apparently we can all breath a little easier. This morning I heard JPL dynamicist Steven Chesley announce that the chance of an impact has dropped to something like 1-in-250,000.

But we're not completely out of the woods. The new computations also reveal a comparable impact risk on the same date in 2068 — and for now there's no way to rule that one out. Says Chesley, "2068 is the new 2036."

The problem is that when asteroids rotate, their orbits change due to a subtle phenomenon, called the Yarkovsky effect, whose consequences for impact predictions have only recently been appreciated. Spin an asteroid one way, and its orbit gets bigger; spin it the other way, and the orbit gets smaller.

We don't know which way Apophis is spinning, but observers are sure eager to find out! David Tholen (University of Hawaii), who's followed this body intently with the 88-inch telescope atop Mauna Kea, thinks he'll have a good shot at getting the answer next May. If that doesn't pan out, Apophis will come within 10 million miles of Earth in January 2013 — close enough (but not too close) for radar ranging to do the job.

If all else fails, we'll have an especially good view of this little interloper in April 2029, when it'll pass just 25,000 miles from us (not much higher than the orbits of geosynchronous satellites). Don't worry: Chesley assures us that there's no chance of an impact then.