Hubble spins an asteroid

By Phil Plait | October 8, 2010 1:29 pm

In 2011, the NASA space mission Dawn will enter orbit around the second largest asteroid: Vesta. This rock is about 530 km (320 miles) across, and is just barely big enough for its own gravity to crush itself into a sphere.

Well, almost. It’s not quite spherical, but it’s close. Since it never gets closer than about 200 million km (120 million miles), we don’t have clear pictures of it. But we need to get data before Dawn enters orbit, so that surprises are kept to a minimum. That’s why Hubble was pointed at Vesta in February, returning some of the best images yet:


I know, they’re still fuzzy, but c’mon! You’re looking at something roughly the size of my home state of Colorado from more than 200 million kilometers away!

And there’s stuff to see. Vesta rotates once every 5.34 hours, and the numbers under each picture represent the rotation angle; think of it like the longitude of Vesta we’re looking at. You can see the variation in color and brightness as it spins: those are real features on the surface of this small world.

Also, in the top row, you can see that one side of Vesta looks flattened. That’s real too: it’s the edge of a huge (450 km (270 miles) diameter) impact crater covering a lot of the asteroid. It got hit with something very large, probably about a billion years ago. Debris exploded outward, and some of it even fell to Earth. Using spectroscopic analysis of the meteorites and of Vesta the two could be tied together, and the age of the meteorites tell us when the impact must have occurred. Also, some other asteroids are similar enough to Vesta that we think they were debris from the event as well. Analysis of their orbits also indicate an age of about a billion years.

So actually, we know quite a bit about the asteroid. But images like this nail down things like its spin axis, which is important to know when putting a probe in orbit. As the spacecraft circles the asteroid, the tug it feels from gravity changes as the shape of the asteroid below changes. If we can nail down the spin axis (the north and south poles) we can be more confident about how the probe will behave while it orbits. And we can also compare the spacecraft’s motion with models made with images like this to improve our models, so future spacecraft can benefit too. And a final bonus is that with the spin understood better, we’ll have a better grasp of the lighting on the surface from the Sun, making interpreting the images returned from Dawn easier.

All in all, like the ones from comet Hartley 2, these images are very important for spacecraft visiting other worlds. The close up pictures and data we get are incredible, but they’re helped a lot by the fleet of observatories we keep back home, too.

Related posts:

Asteroid comparison chart
Vesta interest
Dawn launched

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (32)

  1. NAW

    The video of the rotation is reall great. I can’t wait to find out what the dark patch is. If anything.

  2. Is it possible to get clearer ground-based imagery using radar?

  3. Out of curiosity, why are we going to this body in particular? Is it ease of access? Is something peculiar to this asteroid that we want to study? Was it just next on the list?

  4. Joel

    @Thomas: One of the reasons is that detailed examination of Vesta is expected to reveal more information about conditions in the early solar system. Once it’s examine Vesta for a while, it’s then heading of for Ceres. I think there is probably an element of “next on the list” too – after all, these are the two largest objects in the asteroid belt, but we’ve never seen them in any more detail than these hubble pictures.

    There’s a good overview of the Dawn mission and what it hopes to achieve here:

  5. NAW

    Well reading up on the Dawn craft. It will check out both Vesta and Ceres. They are #1 and #2 in the mass list. And they will give both an icy and rocky “world” to study. And by the looks of it, maybe to check on if the “HED” meteorites are from Vesta.

  6. Now, this is the kind of asteroid Bruce Willis walked on right?


  7. Ceres is the largest asteroid in the asteroid belt; Vesta is the second largest. Together they contain a whopping 41% of the asteroid belt’s mass. Ceres is, in fact, so big — 950km across! — that it qualifies as a dwarf planet. Ceres is particularly interesting in that it’s thought to contain underground liquid water oceans, making it ideal for colonisation. It may even contain life!

  8. Joel

    @David Given: Tut tut. Get with it! Vesta is the largest asteroid in the belt these days. Whopping great Ceres is a Dwarf Planet now, and can hang out with Pluto and Eris and co should it so wish.

  9. See, this is why they shouldn’t cancel shuttle missions. A couple of astronauts with a disposable camera could get better shots. And at most it should take a couple weeks for them to get there and back.

  10. Oli

    @ 8. Cafeen Man

    You do realise that the shuttle isn’t made to travel that far and that it takes half a year to get to Mars alone?

  11. I am really looking forward to learning more about Vesta when Dawn arrives there in 2011. I am especially interested in the volcanism that took place on Vesta shortly after it formed, which is evident by the basalt that covers much of its surface.

  12. NAW

    @ 10. Oli

    You didn’t take Lame Jokes 101 did you?

  13. Cain

    I wonder how far an astronaut could jump on Vesta. Far enough to launch themselves into orbit?

  14. Excellent! People are too blase about this sort of thing, and forget that we are the first generations in thousands of years of history to see things so far away, and develop an understanding about our greater universe. I think these are wonderful, and continuing advances in telescopes will yield even more beautiful results. I also love keeping up with DAWN because of its unique propulsion! Coolness, all around.

  15. Grand Lunar

    It’s a wuzzy world, and it’s getting wuzzier all the time. :)

    Vesta sure looks different than it did in the movie “Meteor”!
    This gives a nice preview of what Dawn will see when it gets there.
    I’m giddy with anticipation of what will be found.

  16. Theobroma Cacao

    Why go to Vesta? To get marooned off it, of course… (

  17. Dave

    How close does Dawn need to be start measurements? It’s already in the neighborhood: Suppose it doesn’t have much long-range imaging capability, though.

  18. Messier Tidy Upper

    @4. Joel Says:

    … Once it’s examine Vesta for a while, it’s then heading of for Ceres. I think there is probably an element of “next on the list” too – after all, these are the two largest objects in the asteroid belt, but we’ve never seen them in any more detail than these hubble pictures.

    & #7. David Given Says:

    Ceres is the largest asteroid in the asteroid belt; Vesta is the second largest.

    Could be mistaken but I’m pretty sure about this – isn’t *Pallas* the second largest asteroid and Vesta the third largest?

  19. Messier Tidy Upper

    Oh well, turns out I was mistaken. Pallas is actually less massive than Vesta although it has around the same diameter.

    Ceres comprises a third – 32% – of the total mass of the asteroid belt with Vesta comprising 9% versus 7% for Pallas.

    With a mass estimated to be 7% of the total mass of the asteroid belt, Pallas is one of the largest asteroids. Its diameter is some 530–565 km, comparable to or slightly larger than that of 4 Vesta, but it is 20% less massive, placing it third among the asteroids. The Palladian surface appears to be a silicate material; the surface spectrum and estimated density resemble carbonaceous chondrite meteorites. The Palladian orbit, at 34.8°, is unusually highly inclined to the plane of the main asteroid belt, and the orbital eccentricity is nearly as large as that of Pluto, making Pallas relatively inaccessible to spacecraft.

    See :



    Vesta, of course, is the brightest asteroid and the only one that is ever visible to the unaided eye. Despite that fact, Ceres, Pallas and also the much smaller Juno were discovered before Vesta was.

  20. Alareth

    Just send the pics to a CSI lab. Once Gary Sinese or Jeff Goldblum says “Enhance” a few times we will have images at sub-millimeter resolution.

  21. Lukas

    unrelated, but I’m sure Phil will love this (2-year old fascinated with astronomy)

  22. Donovan

    While I can’t wait to see the Vesta pictures once Dawn is close, I’m not fooled by these pictures.

    That’s not Vesta, nor is it a typical asteroid. I mean, it’s so obvious. That’s a blueberry cream Jelly Belly jelly bean! In the 83 degree picture, you can just make out their logo. Some astronaut must have been cruising around in the shuttle blasting “Radar Love” with the windows down popping Jelly Bellies and noticed how nasty the blueberry cream ones are, spit it out the window, and now some poor NASA post doc just took a picture of it as it rolled past Hubble.

    I mean, it’s that, or, according to the Law of Dichotomy, there’s a huge band of jelly beans orbiting just on the other side on Mars, in which case we need more funding for manned missions, and the anthropic argument for a creator just won the bet.

  23. Whilst I am certainly interested in Dawn’s encounter with Vesta, it’s the Ceres encounter that really has my attention. A rocky Dwarf Planet much closer than the far out Plutoids, and it has that one patch of much higher albedo just waiting for us to find out more about it.

  24. watch the skies

    Jeff Goldblum is on CSI? I might start watching it again.

  25. Oli

    @12. NAW: I was trolled? Damnit.

  26. Daniel

    Its the Great Potato, Charlie Brown! Love those Hubble images!

  27. The debris from the collision(s) with Vesta makes up one of the larger asteroid families, and they’re spectroscopically distinct from other groups – which makes them really stand out when you plot their orbital elements and include their photometric colors:

    That shows the orbital properties of the asteroids seen by the Sloan Digital Sky Survey: specifically, their inclination vs. their eccentricity. Vertically, the three sets of panels show different subsets in semi-major axis.

    The colors of the points represent the photometric colors measured by the SDSS camera. The Vesta family really stands out in the bright green points.

  28. Doug

    It’s great to see that Colorado is your home state now!

  29. Pete Jackson

    @2 Gumby… Only asteroids that come within a few million miles can be probed with radar. Main belt asteroids like Vesta are simply too far away. The strength of the return reflection of a radar signal beamed at a celestial body drops off as the fourth power of the distance!

  30. Patteroast

    Vesta’s a really interesting place in its own right… while most of the asteroid belt is made up of various rocky and metallic bits, Vesta got hot enough to experience melting, differentiation, and volcanics. And perhaps it was even large enough to be rounded enough to count as a dwarf planet… until we can get the specifics of the gigantic impact basin, we won’t be sure.

    Also, just because Ceres is a dwarf planet, that doesn’t mean it’s not still the most massive member of the asteroid belt.

  31. Messier Tidy Upper

    @ ^ Patteroast : Agreed. Nice comment. :-)

    @23. IMForeman Says:

    Whilst I am certainly interested in Dawn’s encounter with Vesta, it’s the Ceres encounter that really has my attention. A rocky Dwarf Planet much closer than the far out Plutoids..

    Actually, Ceres is much more icy than rocky. As its wiki-page (linked @ #19) notes :

    its oblateness appears too small for an undifferentiated body, which indicates that it consists of a rocky core overlain with an icy mantle.[7] This 100 km-thick mantle (23–28 percent of Ceres by mass; 50 percent by volume[51]) contains 200 million cubic kilometres of water, which is more than the amount of fresh water on the Earth.[52] This result is supported by the observations made by the Keck telescope in 2002 and by evolutionary modelling.

    With its internal structure likely to consist of a dusty outer crust over a thick water ice mantle then a solid inner core.

    Ceres then is more like an ice dwarf planet than a rock dwarf planet.

    Vesta, OTOH, would seem to be rocky in nature – and formerly volcanic at that. I think Vesta is also in the running to make dwarf planetary status as well. So if you want to see an asteroidal type dwarf planet then Vesta will be the one. :-)

  32. @13 Cain:
    According to the back of my envelope, no, an astronaut could not jump off Vesta.

    Assuming a mass of 3 x 10^21 kg and a radius of 265 kilometers (thank heavens for NASA Planetary Fact Sheets), I figure Vesta would have an escape velocity of about 3890 meters per second, while an astronaut would be lucky to do 3 m/s by jumping.

    Vesta’s gravity is about 1/35 of Earth’s gravity, so an astronaut should be able to jump 35 times as high as they could on Earth.


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