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.

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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.

All Eyes on LCROSS
Facility	Location	Aperture	Result
AEOS	HI	3.7 m	No detection yet
Allen array	CA	(radio)	No detection
Apache Point	NM	3.5 m	No detection
CFHT	HI	3.6 m	No detection yet
Gemini N	HI	8.1 m	No detection yet
IRTF	HI	3.0 m	No detection yet
Keck	HI	10.0 m	No detection yet
Kitt Peak	AZ	2.1 m	Sodium detected?
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	2.5 m	TBD
Palomar	CA	5.0 m	No detection
Subaru	HI	8.3 m	No detection
Table Mountain	CA	0.6 m	No detection
GeoEye 1	orbit	1.1 m	TBD
HST	orbit	2.4 m	No detection yet
Ikonos	orbit	0.7 m	TBD
Odin	orbit	1.1 m	TBD

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."

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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.

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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.

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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

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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.

Downtown Washington may be awash with light pollution, but the stars came out last night for an evening of stargazing on the White House South Lawn.

President Obama and his wife, Michelle, greeted a crowd of about 150 middle-school students who'd come to take part in the first-ever White House Star Party. Helping them out were current and former astronauts Buzz Aldrin, Sally Ride, John Grunsfeld, and Mae Jamieson; presidential science adviser John Holdren; and NASA administrator Charles Bolden. That's some guest list!

The president is pressing for dramatic improvement in the quality of U.S. science and math education, and he's now twice urged the nation's youth directly to study hard and reach for the stars. In his opening remarks, the president challenged the assembled students to strive for greatness. "What will your great discovery be?" he asked. "Galileo changed the world when he pointed his telescope to the sky. Now it's your turn."

Standing at President Obama's side were two teenagers who've already made a difference: 14-year-old Caroline Moore, who last year became the youngest person to discover a supernova; and high-school sophomore Lucas Bolyard, who discovered a pulsar in archived radio-telescope observations.

Eight months in planning, the White House Star Party came just in time to jump start two of the International Year of Astronomy's key events: the "Great World-Wide Star Count" (October 9-23) and "Galilean Nights" (October 22-24).

You can watch President Obama's opening statement — and take a quick peek at the Double-Double in Lyra through a Celestron 8-inch telescope — on YouTube.

Phoebe has long been regarded as the black sheep of Saturn's major satellites. For starters, it's got a retrograde orbit — in other words, it travels backward compared to its sibling satellites. Moreover, it's quite dark and lies on the outskirts of Saturn's gravitational grip, 8 million miles (13 million km) out. All of this has dynamicists thinking that Phoebe might have been captured by Saturn long ago.

Just 135 miles (215 km) across, this oddball now has another claim to fame: a ring of its own. Yesterday, at a meeting of planetary scientists in Fajardo, Puerto Rico, Anne Verbiscer (University of Virginia) announced that Phoebe is responsible for an enormous, diffuse ring that envelops its orbit. The band shows up faintly in scans of the Saturnian system taken last February by the Spitzer Space Telescope’s Multiband Imaging Photometer (MIPS).

Collaborating with Virginia colleague Michael Skrutskie and Douglas Hamilton (University of Maryland), Verbiscer was trying to identify the source of the black-as-soot dust that coats the leading hemisphere of Iapetus, the two-faced moon inward of Phoebe that has perplexed astronomers ever since its discovery by Giovanni Domenico Cassini in 1671. "The dark/bright asymmetry on Iapetus was the main motivation for our search," Hamilton notes. The team wasn't sure the dust from Phoebe would be visible, he explains, "but it was certainly worth taking a look!"

The Spitzer scans, made at the deep-infrared wavelengths of 24 and 70 microns, reveal a tenuous belt near Saturn's equatorial plane that's far larger than any of the planet's other rings and tipped 27° with respect to them. According to Verbiscer, the thick band seems to envelop the region 2,300,000 to 11,200,000 miles from Saturn (30 to 150 times the planet's diameter). But it wasn't seen as far out as 15,000,000 miles (200 diameters), making Phoebe the logical source. Either meteoritic impacts are constantly blasting bits off of the moon's surface, or a single modest impact knocked away the equivalent of 1 cubic kilometer of material.

However they escaped Phoebe, countless tiny dust grains are being dragged toward Saturn by subtle gravitational and radiational forces. As they spiral in, they're intercepted by the next moons inward, particularly Iapetus and (probably) Hyperion. "This dust is striking Iapetus like bugs on a car's windshield," Hamilton observes, confirming Phoebe dust as the cause of Iapetus's dark half.

However, Verbiscer cautions that the black-as-coal hemisphere not just a dusty coating raining out of the sky, because Phoebe and the dark side of Iapetus are not a spectral match. Instead (or in addition), the hypervelocity peppering could be causing ice on Iapetus's surface to erode and disappear over time, leaving behind what little dust might have been already mixed in with it.

Verbiscer, Skrutskie, and Hamilton report their findings in the October 8th issue of Nature. NASA's press release about the discovery is here.

Someday we Earthlings may grow used to the idea that small asteroids occasionally slam colorfully but harmlessly into our planet's shielding atmosphere.

For now, however, there's only one — designated 2008 TC₃ — and today marks the first anniversary of its discovery. No bigger than an SUV, this interplanetary interloper revealed itself in images from the Catalina Sky Survey's telescope in Arizona only 19 hours before it exploded over northern Sudan in the predawn darkness of October 7th. Never before had astronomers identified, ahead of time, something about to strike Earth.

That should have been the end of 2008 TC₃'s story — but it wasn't. The big rock self-destructed spectacularly at an altitude of 20 miles (37 km) and, against all odds, dropped fragments on the rubbly Nubian desert. A search effort, led by Peter Jenniskens (SETI Institute) and physicist Mauwia Shaddad (University of Khartoum), recovered dozens of black-as-charcoal lumps along an extended west-to-east path (called a strewnfield). These fragments are collectively named Almahatta Sitta, which is Arabic for "Station 6", the Sudanese rail stop nearest the fall site.

Since then, meteorite specialists around the world have tried to understand just what fell out of the sky a year ago, and yesterday a gathering of planetary specialists in Puerto Rico heard the latest assessments of what one attendee called "a sample-return mission for the cost of a plane ticket to Sudan."

The collected stones are ureilites, dark carbon-enriched rock that once was at least partly molten. But even among ureilites, which comprise only 1% of all meteorite falls, Almahata Sitta is both weird and unique. It's a fragment of an asteroid initially some 120 miles (200 km) across that melted, then got smashed apart, then reassembled into a hodgepodge of loosely welded fragments. "You could crush it in your fist," observes Michael Zolensky, who analyzed pieces of Almahata Sitta at NASA's Johnson Space Center.

Jason Herrin, his NASA-JSC colleague, reports that that pockets of carbon within the meteorites must have been cooked to at least 2100°F (1150°C), before cooling rapidly. Another assessment by Andrew Steele (Carnegie Institution of Washington) found microscopic diamonds embedded within some of the carbon. Yet the fragile stones contain far less organic material than do other carbonaceous meteorites that haven't been heated so much.

Meanwhile, three Czech researchers led by Peter Scheirich have deduced both the shape of 2008 TC₃ ("It looked like a loaf of bread with a flat side," quips Jenniskens) and how it was tumbling just before striking Earth. Although seemingly chaotic, the asteroid's motion resulted from twirling around two different spin axes every 99 and 97 seconds.

Scheirich showed a mesmerizing animation of how the asteroid would have looked up close as it tumbled toward its demise. His analysis relied heavily — frankly, it wouldn't have been possible — without a 2-hour-long sequence of images taken every 4 seconds by Marek Kozubal and Ron Dantowitz of the Clay Center Observatory in Brookline, Massachusetts. As they tracked 2008 TC₃ in its final hours of existence, the asteroid's brightness flared and dimmed by a full magnitude as different its faces were facing Earth.

Jenniskens and Shaddad plan to revisit the scene of the crash in two months, as part of a workshop about the unlucky asteroid and its lucky survivors at the University of Khartoum.

We're kinda proud here right now. J. Kelly Beatty, a Sky & Telescope editor since 1974 (and who writes many of the news stories in this space), today received the first Jonathan Eberhart Planetary Sciences Journalism Award at the annual meeting of the of the Division for Planetary Sciences (DPS) of the American Astronomical Society (AAS).

Kelly has been S&T's solar-system specialist for longer than some of our staffers have been alive. He received the award for his article “Reunion with Mercury,” the cover story of the May 2008 issue, but there's a lot of history behind that. Kelly has written more than 100 feature-length articles for us and countless shorter news reports. His work has also appeared in many newspapers, he's a frequent astronomy explicator on radio and TV, he's principal author of the acclaimed textbook The New Solar System, and he's very active in light-pollution control both here in the Boston area and as a board member of the International Dark-Sky Association. Among other things.

This is Beatty’s second award from the DPS. In 2005 he won the Harold Masursky Award for Meritorious Service to Planetary Science. And, earlier this year, the American Geophysical Union gave him its 2009 Robert C. Cowen Award for Sustained Achievement in Science Journalism.

Way back in February, plans were afoot to have President Obama and his family host a star party at the White House as part of the International Year of Astronomy. Eight months later, it's going to happen. On October 7th some very carefully chosen amateur astronomers will be giving the Obamas and 150 children a tour of the heavens from the White House South Lawn.

A press advisory, issued yesterday, notes that on Wednesday evening "the President and First Lady will host an event at the White House for middle-school students to highlight the President's commitment to science, engineering and math education as the foundation of this nation's global technological and economic leadership and to express his support for astronomy in particular — for its capacity to promote a greater awareness of our place in the universe, expand human knowledge, and inspire the next generation by showing them the beauty and mysteries of the night sky."

Wow.

This stellar event is the brainchild of Audrey Fischer, a Chicago-area amateur who imagined uniting children around the world with one big stargaze. Early this year, her head full of stars after a visit to Mauna Kea, she fired off an email to the White House to pitch the idea. "Every astronomer, teacher, and child I talked with [is] so enthusiastic," she wrote. "They are just holding their breath for your response."

You can imagine how many entreating emails West Wing staffers must slog through each day, but something about this one clicked. Desiree Rodgers, the White House's social secretary (in charge of events like the annual Easter-egg roll) called Fischer for more details. Hundreds of supportive messages poured in from around the country, and a volley of phone and email exchanges between Fischer and various Administration officials followed. The idea had gotten traction.

Fischer's original hope was to hold the star-studded star party in early April, to coincide with the IYA's "100 Hours of Astronomy." But the months dragged on with no confirmation. Was the early momentum waning?

In July, I heard presidential science advisor John Holdren, who heads the Office of Science and Technology Policy, tell a gathering of space enthusiasts that President Obama was committed to jump-starting innovation in science and technology and that engaging young people was key to this plan. I sidled up to Holdren afterward and broached the star-party idea. He was aware of it, thought it was a great idea, and felt sure it would happen.

IYA organizers had suggested a couple of celestially favorable dates, September 26th and October 23rd (the latter to coincide with the IYA's "Galilean Nights"). Ultimately the White House and OSTP picked October 7th — not optimum for a kid-friendly star party because there'll be no evening Moon. Jupiter will be up (a plus) and there's a whopper of an Iridium flare (magnitude -8) that night. But little else in the night sky will be obvious from our nation's light-drenched capitol.

The irony in all this is that the White House handed off the event's coordination to NASA Headquarters, leaving the IYA team completely in the dark, so to speak. And get this: Audrey Fischer didn't receive an invitation to attend!

Nonetheless, it should be a wonderful event. I hope President Obama uses it not only to fire up the next generation of amateur and professional astronomers, but also to raise awareness about light pollution and the energy waste it represents.

So how can you join in the festivities, albeit vicariously? Details are still sketchy, but apparently President Obama will kick-off the event at about 8 p.m. Eastern time with a brief address that will be streamed live by the White House and by NASA TV. Plans include viewing through more than 20 telescopes; presentations in portable planetariums; and various hands-on activities. (If it's cloudy, there'll likely be a secondary site to host the event indoors, perhaps the U.S. Naval Observatory.)

Meanwhile, IYA organizers are scrambling to organize local star parties nationwide at the same time, and to get some linkage to upcoming events like the "Galilean Nights" and the "Great World Wide Star Count".

No matter what the outcome, it's impressive that President Obama is showing this much interest in science generally and astronomy in particular. Another president, Thomas Jefferson, was well known for his scientific curiosity, and a brass telescope is prominently displayed at Monticello, his Virginia home.

I wonder how many other presidents have done some stargazing. Can any of you help me compile a list?