Asteroid Vesta - Images from the Dawn Spacecraft

With the New Horizons spacecraft hurtling toward its 2014 encounter with Pluto, and with the Dawn spacecraft now at its most up-close and personal encounter with Vesta, we are in the process of learning scads of information about two objects that are among the poorest understood and least explored bodies in the Solar System.

Before NASA's Dawn settled into orbit around the asteroid Vesta—the second largest object in the Main Asteroid Belt, after the Dwarf Planet Ceres—we knew very little about it. That it is mega-mountain of rock 330 miles across that rotates rather quickly in space and is slightly egg-shaped, these things we knew—but not much more.

What Dawn has revealed to us, however, is a tiny world with unexpected complexities, inside and out.

Inside, Vesta's anatomy may not be unlike Earth and the other Terrestrial planets, which all developed cores heavy with iron and mantles and crusts made of lighter silicate rocks when they were young and molten. This "differentiation" occurs for the same reason that gold particles sink to the bottom of a gold-pan as a prospector shakes the water-sand slurry back and forth: the gold is denser, the sand lighter, so the materials separate.

Outside, Vesta's surface offers amazing landscape vista opportunities for a future robot lander or astronaut: complex topography of valleys, cliffs, troughs, ridges, and a huge mountain, with elevation differences deviating above and below the global average elevation by as much as 15 miles—that's three Mount Everests, or two Marianas Trenches!

Parts of the surface resemble some of the basaltic formations of cooled lava in Hawaii, suggesting that, long ago, there may have been active volcanoes on Vesta, spewing out lava to shape the young surface.

What a sight it must have been—and it makes me smile when I think about the children's book "The Little Prince." My favorite part of that story was the description of how the Prince, on his little asteroid world (which was only twenty or thirty feet across, I'd guess), cooked his meals on a frying pan held over a miniature volcano, which he made sure to keep clean and functional with a periodic cleaning using a giant Q-tip….

All of these revelations—the core/mantle differentiation, complicated geography, possible tectonic features, and signs of past volcanism–have prompted some scientists to ask, should Vesta be reclassified as a Dwarf Planet, along with Ceres, Pluto, and the others thus dubbed?

I have on my desk at work a letter from a 3rd Grader. It starts, "I think Pluto should be a planet (not a Dwarf Planet)…." The letter continues in richer detail and quite a bit of passionate defense of Pluto, but I was struck by the fact that this 3rd Grader was, at the time Pluto was originally "demoted," three years old. (And some thought the Pluto controversy would end with the previous generation of kids….)

But it did get me wondering. If Dawn has changed our view of Vesta from a mere large asteroid to something maybe worthy of promotion to Dwarf Planet, what might New Horizons do to our current view of Pluto? I'm not suggesting the International Astronomical Union will reinstate Pluto as a planet when we get our first up-close images of its surface—after all, no matter what Pluto's surface may hold in store for us, this Dwarf Planet can't meet one of the three conditions for planethood: being massive enough to clear the region of space in which it revolves. Alas, Pluto shares its orbital space with other objects.

But I fully expect that New Horizons will change our perspective on Pluto, as Dawn is doing for Vesta. The more we learn of the rich details of mysterious places like these, the more, I think, we regard them as "worlds"—regardless of their classification as asteroid, dwarf planet, or planet.

Asteroid 2005 YU55 - Radar image taken in 2010 - Credit NASA/Cornell/Arecibo

At about 1,300 feet across, this roughly spherical, charcoal-black space rock would give us quite a wallop if it were to hit the Earth. A bit larger than a typical football stadium (including a bit of the parking lot), if this asteroid were to strike Earth's ocean a powerful tsunami result, and if it struck land, a city-sized hole in the ground. Not to mention a lot of fireworks.

Fortunately, the asteroid's trajectory is well known, and poses no threat to us (at this time).

Asteroids and comets that can come close to the Earth—Near Earth Objects, or NEOs—have been a concern to life on Earth since it began. From the end of the "era of heavy bombardment," when the young Earth endured frequent impacts by asteroids and comets, large and small, debris leftover from the formation of our Solar System still meets up on occasion with our planet. Craters from past large impacts can be found today, camouflaged by millennia or eons of erosion, sedimentation, and tectonic activity—Earth's scar-healing processes.

The crater left by a 10-mile-sized asteroid (that would be the stadium, parking lot, and the surrounding major metropolitan area) believed to have contributed to the demise of the dinosaurs lies hidden and buried at the tip of the Yucatan Peninsula: the Chicxulub crater. (No, Chicxulub is not an all-women car service station….) Other craters masquerade as round lakes and other landscape sculptures.

And some are quite candidly impact craters, like "Meteor Crater" near Winslow Arizona. When I was in the Peace Corps in Cameroon, my house was 2 kilometers from a round lake that is apparently a meteorite crater. (That's Lake Ejagham; check it out at 5.750000 degrees north latitude and 8.987778 degrees east longitude.) Lake Ejagham is about a kilometer in diameter and 60 meters deep (not counting sediment infill). The meteorite that created it wasn't nearly that big—probably the size of a very small house….

Now imagine an object the size of asteroid 2005 YU55 striking Earth, land or sea. It wouldn't cause our demise—except for unfortunate bystanders—but it would create havoc around ground zero.

And even though 2005 YU55 will not hit the Earth on November 8, all NEOs that pass that close (within the Moon's orbit) are considered near misses, and are scrutinized by the "eyes of the Earth": radio dishes and optical telescopes across the planet.

Chabot's own NEO observing team will aim the eye of our 36-inch telescope, Nellie, on the asteroid and measure its trajectory, contributing to our knowledge of this particular NEO's orbit and improving our ability to predict its future passes.

This time, it's a mere field goal.

Vesta, image from NASA's Dawn spacecraft

Ion thrusters full! Set us into a standard orbit, Mr. Sulu….

Well, I don't know if any of the helms-persons at NASA are named Sulu, but we have indeed achieved orbit—that is, NASA's Dawn spacecraft around the large asteroid Vesta.

I wrote about Dawn and Vesta not long ago, before the spunky little ion-driven robot arrived there. Since then, Dawn has reached its first destination, 117 million miles from Earth, entering a 9,900 mile orbit around Vesta on July 15th. Science observations are expected to begin in early August, but already Dawn has sent back wonderful preliminary images showing details never before seen.

Vesta's surface may bear features and materials among the oldest in the Solar System. Already we can see that Vesta is pock-marked and scared by impacts incurred over the eons. Similar to how a forensic scientist may determine the sequence of events that occurred at a crime scene by studying the physical evidence left behind, the scars and residues on Vesta will help paint a picture of conditions throughout the Solar System's history.

Almost as cool as its science mission is Dawn's propulsion system. To use a term from a certain Smith and Jones movie, it's "the New Hotness." Technology first demonstrated on NASA's Deep Space 1 spacecraft, Dawn's engine is the first solar electric ion propulsion system used on a purely scientific spacecraft. Using electrical power generated by solar panels, Dawn's engine ionizes xenon atoms and accelerates them with an electric field, squirting them out the back of the engine to produce thrust–similar to a balloon-powered car or rocket toy propelled by spurting air. And though a conventional chemical rocket can produce much stronger thrust, Dawn's ion drive, operating with high efficiency and over longer periods of time, achieves up to 10 times the velocity change for an equivalent amount of propellant.

(As a sign of the technological times, in one episode of the original Star Trek series, Scotty was awe-stricken by an advanced alien spacecraft that used ion propulsion. Ironic; what today's space explorers wouldn't give for warp drive….)

Dawn will spend a year orbiting and studying Vesta before it moves onto its second target, Ceres, to harvest its secrets.

Vesta is now the largest known asteroid in our Solar System. It was second fiddle to Ceres for a long time, but back in 2006 when Pluto got "demoted" to dwarf planet status, Ceres' status also changed—promoted or demoted, take your pick. Sure, Ceres is now in the more exclusive club of the dwarf planets, but it's the smallest of that group, whereas when it was an asteroid, it was the largest, going from big fish in big pond to junior member of the upstairs office team….

So what's Vesta like—what we know about it at the moment, anyway? Vesta is a mega-mountain of rock and dust, somewhat lumpy and potato-shaped, but approximating a spherical object with a mean diameter of about 330 miles–roughly the distance from Oakland to Los Angeles as the ion-driven robot flies. In terms of surface area, Vesta has about twice the real estate as the entire state of California!

Sounds pretty big—and it is—but you'd still need over 20,000 Vestas to make one planet with the mass of the Earth. And if you stood on the surface of Vesta, you'd weigh little more than 2% what you weigh on Earth. Myself, I'd weigh in at a tad under 5 pounds. Presumably that means I could jump a hundred feet into the sky and land again safely.

I don't know about the science, but Vesta sounds like a fun place to me!

Illustration from The Little Prince

We are soon to explore a new world, one that we haven't seen up close before: the asteroid Vesta. NASA's Dawn spacecraft, which has been conducting maneuvers for the past four years to get into position to orbit Vesta, will arrive at the asteroid in early August—a la Star Wars, "Almost there…." What will we find, and why are we even interested in what amounts to a mega-mountain of rock hurtling through space?

I've been intrigued by asteroids since I read The Little Prince in childhood. I loved the whole idea of the Solar System filled with uncounted miniature "personal planets," each with one occupant and all the solitude and spare time one might wish. Never mind that the asteroids in that story (not much bigger than houses, if even that) are too small for hydrodynamic equilibrium to shape them into spheres or to hold onto any sort of atmosphere….

Much attention has been given to the planets as good places to explore, but the smaller bodies orbiting the Sun have a lot to tell us. They are composed of materials that may have been altered very little, if at all, since the earliest times in the formation of the Solar System. They also bear the marks—features of the processes of their formation, scars of collisions—of the eons of their existence.

Dawn's mission to Vesta–and ultimately on to the larger Ceres—might be characterized as a Solar-System-scale geological expedition. Much as geologists may probe a deep layer of rock on Earth to learn about our planet's geological past and evolution, Dawn will be probing Vesta and Ceres to learn about the Solar System's formation and development.

Vesta and Ceres—classified as asteroid and dwarf planet, respectively—are the two largest protoplanets, each quite different from the other in potentially informative ways. Vesta is a dry airless body, while Ceres may contain water (ice) and maybe even a thin atmosphere. Being protoplanets, both objects went through a process of differentiation early in their history, forming a core and a crust not unlike planets do.

As we understand the formation of the Solar System today, both from exploration of our own and observation of other planetary and pre-planetary systems at different stages of development, it all started with the Protosolar Nebula: the cloud of gas and dust that began the long gravitational collapse that ultimately gave birth to the Sun, planets, asteroids, and comets. Little by little, dust particles in the nebula stuck together, forming larger and larger clumps. Eventually, gravity began to play a stronger role in the clumping process, with the larger clumps pulling in more and more dust and neighboring clumps, snowballing ever larger.

Clumps that reached sizes of a mile or so across earned the title "planetesimal," and when planetesimals grew into objects hundreds of miles across, they graduated to the rank of protoplanet. This career ladder climbing went on until most of the raw material had been swept up. At this point, if the snowballing process had produced a Sun-orbiting object that was large enough to pull itself into a spherical shape and also "dominate" the region of space it was in (according to International Astronomical Union requirements), then it could be called a planet. If not, other classifications, like dwarf planet or small Solar System body, might apply…if you have a complaint, register it with the IAU….

In the case of Vesta and Ceres, which are on the order of 300 and 600 miles across, roughly and respectively, their career aspirations in planetary stature building are thought to have been crushed by the formation of Jupiter—perhaps as how a type-A personality with powerful career ambitions might derail a coworker by grabbing all the promotions….

What world might have been if Vesta and Ceres had finished their work and not ended up in the Mail Room of the Solar System? Well, if you took all of the material present in the Main Asteroid Belt today and brought it together into one object, orbiting the Sun between Mars and Jupiter, you would have a sphere probably no bigger than 900 miles across—less than half the diameter of Earth's Moon—so at best it might rate as a dwarf planet.

However, it is believed that most of the original mass of the Main Belt has been lost, scattered to other places in the Solar System by that ambitious Jupiter…so who knows what this world that never was might have been if circumstances had been different?

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A few weeks ago, this asteroid came really close to hitting Earth.

Called “2009 DD45”, the asteroid was estimated to be around the same size as the one that exploded in the atmosphere near the Podkamennaya Tunguska River in remote Siberia on June 30th, 1908, flattening 80 million trees across eight hundred square miles of remote forest. Of course, if an asteroid of this size were to hit a city or in an ocean offshore from a populated area, tens of thousands of people would likely die.

Then, just as the last of the night sky observers were completing their collective sighs of relief, on March 17th, 2009 another Tunguska-class asteroid, 2009 FH, passed by about 53,000 miles from Earth. Thankfully, neither of these asteroids actually hit us. But astronomers didn’t even observe 2009 DD45 until 4 days before its closest approach. It's orbit was calculated and it was determined that it would miss the Earth. But it's likely that asteroids of this size are fairly frequently buzzing by the Earth. And until recently, most of them have been undetected.

In 1998, NASA started the Spaceguard Survey which set out to discover 90% of those Near Earth Asteroids (NEAs) 1 km in diameter and larger. An impact by an asteroid this size would likely cause global destruction and an end to much of life as we know it so it’s definitely reassuring that 10 years after its inception, the Spaceguard Survey had found about 80% (CK) of them. But unfortunately, once we’ve found them, there’s still no international concensus or infrastructure in place in how to deflect or destroy them. But the Survey is limited by its mandate to find those mass extinction-sized asteroids as well as by the size and sophistication of the telescopes that are dedicated to searching the skies.

As former Apollo 9 astronaut, Rusty Schweickart said in a recent phone conversation, "in the process of finding the big ones, you also find a bunch of small ones, and the smaller ones are obviously far more numerous than the large ones." But it will take many more resources and new telescopes to continue searching for and tracking the smaller ones. And unfortunately, once we’ve found them, there's still no international consensus or infrastructure in place in how to deflect or destroy them. Raising awareness and building alliances amongst governments and space agencies is Schweikart's current "mission". He founded the B612 Foundation and Association of Space Explorers to tackle these goals on different fronts.

The message that I hope is conveyed with the Asteroid Hunters TV segment is that we are not immune from asteroid impacts here on Earth. Rusty Schweikart puts it best in a portion of his interview that didn’t make it into the final program:

"Well, asteroids and comets are good news and bad news, you know? But for them we wouldn’t be here, and on the other hand, if we don't actually take some action now, at some point we won’t be here anymore, because there's no question that we will be hit by asteroids, and we’ll probably be hit by, we would be hit by comets as well. Unless, we use the technology that we have and the brains that we have in order to protect the Earth from asteroid impacts, and we can do that. We can basically now, with current technology, assure that no asteroid ever hits the Earth again. That can do any serious damage."
-Rusty Schweikart

Here's a little exercise from Rusty that you can do to get a sense of what we know today about exactly what's out there:

• Go to: neo.jpl.nasa.gov/risk
• See two tables, the first table says "Recently Observed Objects" and the table below says "Objects not recently observed." You’ll notice in the bottom table that Apophis is the 4th one listed.
• Click on "Apophis". At the top you see a bunch of boxes, like the diameter at .27 km, or 270 meters.
• Down below that you see 3 lines, those are the 3 potential impacts. The first one is April 13, 2036. Go over to the right on that line you'll see the column "Impact Probability" is 2.3 x 10-5 – click on that. So there is the probability, 1 in 43,000 of that particular impact.
• Now if you go back to the main table you can do the same thing with every single one of those lines.
• Now go to the very top of the page and hit "Discovery Statistics." Scroll down to a blue and red graph "Known Near-Earth Asteroids". This shows the discovery rate beginning back in 1980 going up to almost current time. Notice the knee in that curve in 1998 – that’s when the Spaceguard Survey began.
• Scroll down to table just below the graph and look across that table to the far right side, to see that a a total of 6166 NEOs (of ALL sizes) have been discovered.

Rusty concludes that, "…what we really care about is not only the things that large, we care about things that can hurt us. Things that can hurt us go down to 40 to 45 meters or so. Instead of there being 940 of them, there are more like 600,000 of them. So the new charge for NASA, which they have so far ignored, is to find 90% of the objects 140 meters and larger by 2020. You can't reasonably set a goal to find everything down to 40 meters because it's just beyond the capability of telescopes and the money available. So NASA, working with Congress, set the goal at 140 meters. Now nevertheless, when you are looking for 140 meter objects, it’s going to take bigger telescopes than the ones to find a kilometer. Therefore we are going to find many many smaller objects as well. So 10 to 15 years from now, instead of that number on the far right hand column being 6000, it will be 1 million."

Watch the Asteroid Hunters television story online.

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The Hoba meteorite in Namibia, Africa, the largest known
meteorite found; approximately the size of 2008 TC3 before
it burned up in our atmosphere.

Wait a moment… an asteroid you say? Hitting the Earth? Isn't that supposed to spell some kind of disaster, such as Dino-slaughter? Isn't that something we send people like Bruce Willis and Clint Eastwood to deal with before it becomes a problem down here on Earth?

Okay, so Asteroid 2008 TC3 wasn't an Earth-killer, but rather a crowd-thriller. It wasn't miles across-not even tens of meters across. It was, perhaps, a few meters in size, similar in volume to mid-size car. In fact, it didn't even hit the Earth's surface, but vaporized in the atmosphere.

Sounds a bit anticlimactic-and that's not the half of it. It's not even a rare event! Objects of this size are believed (and sometimes observed) to enter Earth's atmosphere a few times each year. So what's the blog deal?

The blog deal is this: this is the first time that an object this size has been detected approaching the Earth a significant period of time before actually impacting-in this case, about a day. 2008 TC3 was detected by the Mount Lemmon telescope in Arizona on Monday. The detection was reported to the Minor Planet Center, which collects such observations from observatories large and small (including Chabot Space & Science Center) in order to track and predict possible Earth impactors. In turn, the MPC alerted NASA of the impending impact.

Observers on the ground reported the fireball lit up the skies with the intensity of the Full Moon. A nearby airliner (not in danger, as the fireball exploded tens of kilometers above the ground, well above the airliner's flight path) reported seeing a bright flash.

In a sense, this event was kind of a dress rehearsal for the international system of predicting, and possibly defending against, impacts on Earth by much larger asteroids and comets. We already know of thousands of Near Earth Objects (NEOs-asteroids and comets that cross Earth's orbit and are large enough to cause a catastrophe should they strike the Earth). It is also expected that there are many thousands more that we haven't yet detected, being small enough to "fly under the radar" of our NEO detecting network.

Early detection and sustained tracking of NEOs is key to the protection plan against impact disaster. If we can accurately predict an impact far enough in advance, we could potentially send a spacecraft to it and gently "nudge" it off course and deflect the eventual impact.

So ends the existence of another chunk of rock that had, up to that point, been serenely orbiting the Sun for billions of years…

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Asteroid 35107, captured on Chabot Space
& Science Center’s telescope.

Photo By Conrad Jung and Gerald McKeegan

You must be very quiet; we are hunting…asteroids!

On July 14th, 2008, an almost Hollywood-like drama took place in space nearby: a "double," or binary, asteroid whizzed past Earth, grazing by at a distance of only 1.4 million miles. One of the rocks is over 200 meters across, the other a whopping 600 meters-about half the size of Half Dome in Yosemite!

1.4 million miles may sound like a large distance, but by the standard of big rocks flying by the Earth, that's breathtakingly close. Discovered only last January, this pair of asteroids went from being completely unknown to blasting by Earth's doorstep in only months. Had they actually hit the Earth, they would have caused major devastation at and near the impact site, with very little warning.

Fortunately, there are programs to search for and track these flying mountains-also called "Near Earth Objects" (NEOs)-and I'm very pleased to announce that Chabot Space & Science Center (specifically our 36-inch reflecting telescope, "Nellie") has very recently become an official contributor to the NEO search program of the International Astronomical Union's Minor Planet Center (MPC)! Nellie is designated by the MPC as Observatory G58.

In this MPC program, observatories around the world contribute by searching for and tracking NEOs: asteroids, and comets, whose orbits can carry them close to Earth and which are large enough to cause catastrophic damage should they hit us.

In order to take part in the NEO program, Chabot observers Conrad Jung (on the Chabot staff) and Gerald McKeegan (of the Eastbay Astronomical Society) conducted a four-month program to develop and hone the necessary skills and data processing techniques, as well as to configure telescope equipment, to meet MPC qualifications.

To that end, they observed a set of known asteroids-some NEO's and some "Main Belt" asteroids. (One of these Main Belt asteroids, "Carter 10683," was named for former Chabot board member and president of the Eastbay Astronomical Society, Carter Roberts, who, sadly, passed away earlier this year.)

Chabot's asteroid hunters will begin their tenure of official asteroid observation by verifying the orbits of recently discovered NEOs and reporting the additional observations to the MPC, where it will be used to refine our knowledge of the NEOs' orbits. The next step in the program will ultimately be to hunt for currently undiscovered asteroids.

The process for finding, tracking, and reporting NEO observations goes something like this. With a digital (CCD) camera attached to the telescope, a section of the sky is imaged three or four times in a half-hour period. The images are processed and compared, and any star-like dots that are found to move between one image and the next become suspect asteroids. (The word "asteroid," by the way, literally means "star-like"-so named because through most telescopes asteroids are too far away and too small to appear as anything more than points of light.)

The coordinates of any moving dots are calculated for all of the images they are in, and this information is sent to the MPC to be added to the data from other NEO hunting observatories. From the combined observations of all the observatories, a precision database of the orbits of near-Earth rocks is maintained, and with it NEOs that may pose a threat to the Earth may be identified.

Hunting NEOs may be like searching for needles in a really big haystack-but in jobs like this, the more eyes on the problem the better. Nellie is now one more eye on lookout duty…

Click here for a closer view of the asteroid shown above.

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You may listen to the "An Asteroid's Close Call" radio report online, as well as find additional links and resources.

Amy Standen is a Reporter for QUEST and Radio News at KQED-FM.

latitude: 37.8768, longitude: -122.251

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Victoria Crater on Mars, similar in size to the crater the
near-Mars asteroid 2007 WD 5 would have produced.
Credit: NASA/Mars Reconnaissance Orbiter

The possibility that a sizable asteroid would strike the planet Mars on January 30th temporarily raised the excitement level in the astronomical community to a pretty high level in the last couple of months. We were even toying with the idea of having a 3:00 AM Mars Bashing Party at Chabot that morning.

At one point astronomers had given odds of 1 in 25 that asteroid 2007 WD 5, newly discovered in November, would collide with Mars–which are astronomically great odds for this sort of thing. Alas, further observations refined our knowledge of the big rock’s trajectory, and the probability declined, hitting rock bottom (0.0%) by January 9th.

Why blog about a non-event? I see it as an opportunity to talk about big rocks bashing planets in general–specifically, the Earth.

While we haven't witnessed an event like this one (a big impact on a solid, Earth-like planet), we have examined the remains of past events, on Earth as well as other planets and moons—such as the hole in the Arizona desert called "Meteor Crater," an impact basin roughly the size of what might have been gouged out on Mars by 2007 WD 5. And compared to the asteroid that is believed to have caused the extinction of the dinosaurs, the Meteor Crater impact was a pipsqueak!

Smaller objects hit the Earth, or its atmosphere, all the time: meteors and meteorites. Fortunately we haven’t experienced a larger impact for a very long time. There was a significant impact of some kind in 1908, over Siberia–but luckily that wasn't a major catastrophe.

Nevertheless, the possibility of a big impact on Earth is something to take seriously. NASA certainly does. They even have a program for it: the Near Earth Object Program, whose goal is to detect and track Near Earth Objects (NEOs) in order to warn of those that might eventually collide with the Earth. A NEO is defined as an asteroid or comet whose orbit carries it close to Earth. The program searches for NEOs that are 1 kilometer in size or larger–objects that would cause catastrophic local devastation and "severe global consequences."

Thus far, over 5,000 NEOs have been found, almost 800 of them 1 kilometer across or larger–and it is expected that there are plenty more out there that we haven't found.

So, is this a good idea? Do we really want to know that the end of the world is going to occur on such and such a date in the near future–or would it be better not to know, living our daily lives in blissful ignorance right up to the last, Earth-shattering day?

Well, whatever your philosophical approach to that question might be, there is a practical side to the NEO Program. If we can predict a NEO collision with enough advance warning, there may be something we can do to avert disaster. For example, we could send Bruce Willis out to destroy it… .

Seriously, though, NASA is working on methods of diverting the course of a NEO, possibly with a spaceship that acts as a sort of tug boat, gently nudging the NEO off course far enough in advance of the impact to make it eventually miss the Earth.

This month, however, Mars 1, asteroid 0. The Martians are quite relieved…

Benjamin Burress is a staff astronomer at The Chabot Space & Science Center in Oakland, CA.

latitude: 37.8768, longitude: -122.251