The Sky is Not Falling

There was a time, way back in the 1990s, when the news media would get really frothy every time a newfound asteroid had even a slight chance of hitting Earth. I remember clearly the saga of 1997 XF11 (now a numbered asteroid, 35396), which for a few uncertain weeks after its discovery had a 1-in-900 chance of striking Earth in 2028. But once some archival images were found and the orbit recomputed, the impact probability went to zero.

Apophis and Earth in 2029
On Friday the 13th in April 2029, a 1,000-foot-wide asteroid named Apophis will pass close enough to Earth (within 20,000 miles) to briefly appear as a 3rd-magnitude star in the night sky.
Dan Durda
In the aftermath of this false alarm and others since, I would have thought that we in the news media (and I use that term advisedly) had learned enough to temper our reporting on such matters.

Apparently not.

This past week the obscure Spanish Foundation for Science and Technology posted a story about a research paper co-authored by Spanish scientist Maria Eugenia Sansaturio (University of Valladolid). The work involved the numbered-but-unnamed asteroid 101955, which was initially designated 1999 RQ36 when discovered by the LINEAR survey telescope. This asteroid's cumulative risk of striking Earth, the report announced, is about 1 in 1000 (0.1%) between now and the year 2200 — with the most likely target date coming in 2182. Given that it's a third of a mile (0.56 km) across, this object would surely do global harm if it hit.

So why am I not worried, and why shouldn't you be? For one thing, even though the paper (whose lead author is University of Pisa dynamicist Andrea Milani) appeared in the respected journal Icarus, it was published without fanfare last October — it's hardly breaking news. Second, you need to read the paper to understand the authors' intent.

Predicting doomsday might be easy for prophets, but it's a lot harder for solar-system dynamicists. When a threatening asteroid is discovered, usually its orbit is known too poorly, even after an intense observing effort, to compute credible impact probabilities more than a few decades out.

Radar images of asteroid 101955 (1999 RQ<sub>36</sub>)
NASA's giant antenna at Goldstone, California, acquired these radar images of asteroid 101955 (1999 RQ36) on September 21, 1999, 10 days after its discovery. Earth is toward the top, and each view is a map of the energy bounced off the hemisphere illuminated by the radar beam. The two-way travel time yields a precise distance to the asteroid, which in this case was accurate to within 62 feet (19 m) despite its being 1.4 million miles away. Click here for details about this observation.
R. Hudson / S. Ostro / L. Benner
In that respect, asteroid 101955 is an unusual case. Thanks to hundreds of careful optical measurements and radar observations made during two close passes, astronomers know the size of its orbit more accurately (to within 20 feet) than that of any other asteroid. As the orbital uncertainty drops, the predictive confidence goes up.

But the point of the article was to explore the validity of impact probabilities made centuries (not just decades) in advance. To do that with any confidence, dynamicists must have more than just a precise orbit in hand. They also need to know the object's shape and surface characteristics in order to calculate the Yarkovsky effect, a subtle interaction caused by sunlight falling on a rotating space rock. Milani's team estimates that this force might be altering the semimajor axis of the asteroid's orbit by more than a mile (2 km) per decade.

Using a best guess of the effect's accumulated nudging over time, the researchers discovered that in 2060 this particular asteroid slips past Earth about a half million miles away. The problem, they explain, is if it goes by just so, passing though a dynamical "keyhole" less 1 km wide, then its chances of striking Earth in 2182 go up dramatically. All this assumes the authors have computed the Yarkovsky effect correctly.

So what should we do? Sit tight, and keep an eye on NASA's impact-risk page. Asteroid 101955 next comes our way next year, passing about 16 million miles from us (as a 20th-magnitude blip) on September 11, 2011. Radar observations made around that time should settle to what degree, if any, the Yarkovsky effect is in play. Chances are excellent — at least 999 in 1,000 — that in time a future impact with Earth will be ruled out.

OSIRIS-REx spacecraft
If approved next year, a spacecraft called OSIRIS-REx (short for Origins Spectral Interpretation Resource Identification Security Regolith Explorer) will land on asteroid 101955 (1999 RQ36) in 2020 and return a sample of its surface to Earth.
Univ. of Arizona / NASA-GSFC / Lockheed Martin
Finally, there's a effort under way to see this asteroid up close and personal — even bring a sample of it back to Earth — in the not-too-distant future. Because it's got an extremely dark and presumably carbon-rich surface, 101955 (or 1999 RQ36, if you insist) has likely remained unaltered since its formation 4½ billion years ago. This would-be Rosetta Stone of early solar-system history is the destination of a proposed mission called OSIRIS-REx.

If picked over two competing proposals by NASA managers next summer, OSIRIS-REx would launch in 2016, land on this dark, worrisome asteroid in 2020, and return to Earth in 2023 with up to 4½ pounds (2 kg) of its surface material.

12 thoughts on “The Sky is Not Falling

  1. astronomer46

    Almost no one now alive that can read and understand the article will be alive in 2082, nevermind 2182. There’s no sit back and relax with this one; just ignore because we won’t be around to care.

  2. JFET

    Now I am worried for “the most intense solar maximum in fifty years”. It will affect a lot of things, including 101955. What about the solar maximum effect in 101955 orbit? And the other Solar phenomena from now until 2182?

  3. SC Astronomer

    Sensationalism sells air time and ad space. No one will be interested if a leading news outlet carried the headline “Asteroid has 99.9% Chance of Missing Earth.”

    Just remember the old adage, “If it bleeds, it leads.”

  4. Phil

    I wish that Brian Marsden & Co. would get out of the habit of announcing (possible) impact dates /before/ an orbit is firmly determined. If a preliminary orbit looks threatening, you certainly need to get pre-discovery images, and possibly follow-up images, but there’s no need to alarm the public by announcing the date and time of The End. Astronomers can be asked for images of a certain area at a certain time, without being told that there’s a possible impact. They’ll understand what it’s for. The sensationalist infotainment complex doesn’t need to be told about preliminary orbits and impact dates — they don’t understand anything about probabilities, and exist merely to alarm the public. Just wait to say anything until an impact is found to be /definitely/ highly probable.

  5. Jon Hanford

    “I wish that Brian Marsden & Co. would get out of the habit of announcing (possible) impact dates /before/ an orbit is firmly determined.”

    I don’t think Brian Marsden was involved with this study. He is not listed as a coauthor on this paper. Besides, I think he’s personally familiar with the ruckus a false positive report would make.

  6. A. A. Szautner

    The remarks by Phil are EXACTLY why any article like this may be necessary. It is clear he entertains the tactic of blaming the weather forecaster for a storm, or the messenger for delivering the news.

    Phil wants astronomers to refrain from announcing what they find…because he figures that the public is too dumb to understand anything as obtuse as a one-in-a-thousand probability.

    And then he pretends to have made a positive statement in favor of science.

    If THIS is the kind of reader you are addressing with your article, you had better start composing a more comprehensive treatment from square one.

    From what I’ve increasingly read elsewhere, such a tract would be enormously more beneficial – compared to the tiresome tennis-ball volley bounced back which we see here – to explain to readers how the popular hype has nothing to do with what’s going on in the dissemination of a scientific finding except $$$.

    Phil, for example, appears to be under the peculiar impression that Brian Marsden is somehow to blame. This sort of thinking seems to be a growing infection in the population at large: to people like Phil, the problem isn’t associated with the evidence. They would much rather attach blame to a person. But Marsden isn’t responsible for the orbits he catalogues.

    Set people like Phil straight first – then go on to instruct your readers on how to distinguish the difference between the announcement of a scientific finding and the popular hype which is so bothersome that you find it necessary to revisit and redebunk it dozens or even hundreds of times over the next several decades as we discover more potential Earth impactors.

  7. bw

    You are right, I plan on being dead in 2082, I’d be well over 100. That is why I don’t care if the current sunspot cycle affects 101955. BUT, I do care if this IS the biggest solar maximum in the past 50 years because I want F2 layer propagation on the 6 Meter amateur radio band.

  8. Richard Kowalski - Catalina Sky Survey

    Thanks for posting this to a wider audience Kelly. As with most of the information that reaches the main stream media, this was another unnecessary story, but one that is of minor interest to the astronomical community. The fact that this story made it into the popular media is strange indeed. Impact threats rise, fall and nearly always disappear as more observations come in. If OSIRIS-Rex does get funding and eventually flies, we will know no later than 2022 that this object is an impactor, or (most likely) is not.

    BTW, Brian Marsden is not involved in this story at all, and in fact retired as Director of the Minor Planet Center several years ago.

  9. Enrico the Great

    The threat of impact of course is real, and the continued search for potential impactors of course must continue so that we may have sufficient lead time to do what may be possible to do.
    Still, the almost unavoidable lame stream media sensationalism attendent on this subject is just as disturbing as the neo-catastrophist trend in science evident since circa 1980.
    Sensationalised science reporting helps no one and certainly is detrimental to the considered discussion of a real threat.

  10. Phil

    I’m disappointed that Sky+Tel has chosen not to remove AAS’s intemperate and hysterical personal attack, despite my having reported it some 24 hours ago. For the record, I’m not “blaming” the messenger for the message. I’m just pointing out that it’s a bad idea to tell the GENERAL PUBLIC that we’re in the crosshairs of some space rock, until its orbit has been confirmed and there’s high probability that it’s going to pay a visit. There are ways to get pre- and post- discovery images, to confirm the orbit, without unduly alarming the dimwitted.

    As for bringing in Brian Marsden’s name, I don’t know if he is involved with this particular report, but he has a long history of prematurely releasing “We’re all doomed!” announcements, invariably followed up a few days later by “Never mind!”. This only engenders disrespect for science in general and astronomy in particular. Some day, astronomers /will/ find a rock with our name on it, and the public (and policymaker) reaction will be “Oh yeah. Yawn. Chicken Little is at it again. Wonder what’s on /American Idol/ tonight?”.

  11. Peter WilsonP Wilson

    That’s too bad. If The Big One were coming our way, we could stop worrying about global warming, dwindling natural resources, rising sea-levels, war in the Middle East, habitat loss, top-soil erosion, desertification, fishery collapses, jelly-fish explosions, etc, and unite against a common enemy. With no unifying threat from the outside…we’re doomed to in-fighting and back-stabbing [sigh].

  12. Whataglass

    I love it that the authors set out to show that predicting orbits is a nightmare when they get too far out in time, but that the message seen in the press was that an impact was coming. Alas, crazy projections are not new, as you can see in the quote below from “Life On The Mississippi” by Mark Twain (Chp. 17)…

    In the space of one hundred and seventy-six years the Lower Mississippi has shortened itself two hundred and forty-two miles. That is an average of a trifle over one mile and a third per year. Therefore, any calm person, who is not blind or idiotic, can see that in the Old Oolitic Silurian Period,’ just a million years ago next November, the Lower Mississippi River was upwards of one million three hundred thousand miles long, and stuck out over the Gulf of Mexico like a fishing-rod. And by the same token any person can see that seven hundred and forty-two years from now the Lower Mississippi will be only a mile and three-quarters long, and Cairo and New Orleans will have joined their streets together, and be plodding comfortably along under a single mayor and a mutual board of aldermen. There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.

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