Tag Archive for 'asteroids'

Dawn arrives at Vesta!

(I was going to call this post “Dawn breaks at Vesta” but that might have given the false impression that Dawn literally broke in orbit and isn’t working anymore 😉 )

Dawn successfully entered Vesta orbit in the weekend, and has returned the first pictures from Vesta orbit!

Vesta! (Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA)

The big lump in the middle of the asteroid is actually the central peak of a massive crater caused by an impact that literally blew away most of the protoplanet’s southern hemisphere! There are all sorts of interesting things to see here – lots of bowl-shaped craters, grooved/scallopped terrain in the big crater floor, and what looks like a huge cliff marking part of the rim of the big crater!

There’s also a very nice image showing another view of Vesta’s ‘south pole crater’, along with other asteroids that we’ve sent spacecraft to shown to the same scale:

Vesta, with other asteroids (Image credit: NASA/JPL-Caltech/JAXA/ESA)

Vesta is about 530 km in diameter, so it’s pretty large for an asteroid – it’s the third largest in the asteroid belt – and is far bigger than Lutetia, which was previously the record holder for ‘largest asteroid visited by a spacecraft’. Dawn will move on to visit Ceres next year, which is the largest asteroid in the asteroid belt and (unlike Vesta) is actually spherical too.

We’ll see more of Vesta as Dawn maps it from orbit over the next year – this only the beginning, and I’m very excited to see what else will be revealed! (You can find out more about the Dawn mission at its official website)

Approaching Vesta!

Vesta! Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

On July 15th, NASA’s Dawn spacecraft will be entering orbit around the asteroid Vesta – and I’m really looking forward to it! This is a new frontier – while we’ve seen a few small asteroids (e.g. Ida, Gaspra), we’ve never seen a big asteroid up close, and Vesta is the third largest asteroid in the asteroid belt between Mars and Jupiter (it’s also the second most-massive after Ceres, which will be visited later by Dawn). We’ve also found several meteorites on Earth that we think were blasted off from Vesta’s surface by impacts on the asteroid – these indicate that Vesta should have differentiated into a rocky mantle and metallic core, and I’m curious to see if there is evidence of volcanic activity on its surface (my Ph.D. supervisor published some papers about Vesta’s early history, and some of his interest and enthusiasm about it has rubbed off on me!).

Asteroids are interesting beasts – they’re mostly found in the space between Mars and Jupiter, and are remnants from the formation of the solar system. The rocky planets in the solar system formed by accretion in the solar nebula about 4.6 billion years ago – put very simply, dust grains clumped together due to gravity to form planetesimals, which themselves clumped together to form protoplanets, which then clumped together to form larger planets. However, Jupiter’s gravity affected (and still affects) the orbits of nearby objects, which prevented the asteroids from accreting into planets. As a result of this, we now have a band of asteroids between Mars and Jupiter – it’s essentially debris that was never allowed to form into a planet. What’s more, if you could combine all the asteroids currently in the asteroid belt, the resulting object would be smaller than our own moon (part of this is due to the fact that many asteroids have been ejected from the belt by gravitational interactions or destroyed by collisions)! Since we’ve not seen a large one up close before, a lot of planetary scientists will be interested to see what Dawn reveals at Vesta (and later when it moves on to orbit Ceres, which is the largest asteroid and also a dwarf planet).

As Dawn has been approaching Vesta over the past few weeks, features have been slowly coming into view that we couldn’t see from Earth. The latest picture (shown above) hints at interesting features – for one thing, there don’t appear to be an awful lot of large craters visible, which would imply that its surface may be young (possibly evidence for volcanic resurfacing?). Some curvilinear features are also visible in the southern hemisphere – maybe they’re tectonic in origin, or perhaps they’re something else (crater-chains? flow fronts?). Right now it’s all very tantalising, but we’ll find out more when Dawn goes into orbit in a few days!

Emily’s Asteroids and Comets montage

I’m working on another science post of my own, but in the meantime I thought I’d share this rather awesome montage that Emily Lakdawalla compiled over at the Planetary Society Blog, which is well worth following if you’re into solar system exploration. It shows all the asteroids and comets that have been visited by spacecraft as of November 2010, including Comet Hartley 2. The really nice thing is that it shows them all at the same scale, so you can see the differences that size makes to thinks like crater size (I think Mathilde is roughly the size of Greater London).

There’s a much larger version of the image available on the Planetary Society page that’s definitely worth checking out too, that shows the little ones in more detail – though be warned, the image is huge!

Comets and Asteroids, by Emily Lakdawalla

Credits: Montage by Emily Lakdawalla. Ida, Dactyl, Braille, Annefrank, Gaspra, Borrelly: NASA / JPL / Ted Stryk. Steins: ESA / OSIRIS team. Eros: NASA / JHUAPL. Itokawa: ISAS / JAXA / Emily Lakdawalla. Mathilde: NASA / JHUAPL / Ted Stryk. Lutetia: ESA / OSIRIS team / Emily Lakdawalla. Halley: Russian Academy of Sciences / Ted Stryk. Tempel 1, Hartley 2: NASA / JPL / UMD. Wild 2: NASA / JPL.

(if you want to comment on it, go over to the Planetary Society Blog and tell Emily! 🙂 )

Fun with asteroid impact simulators!

Meteor Crater, Arizona (credit: USGS)

Barringer (Meteor) Crater, Arizona (credit: USGS)

For those who like to attempt to destroy the earth with asteroids, there’s a new asteroid impact simulator online at: http://www.purdue.edu/impactearth/

I just entered a 10 km nickel/iron asteroid into the calculator, hitting crystalline rock (so… Canadian Shield?) at an angle of 90 degrees, at a (admittedly fast) velocity of 30 km/s, and got it to calculate the effects felt 1000 km away. (For comparison, 1000km is about the distance between Vancouver and Calgary in Canada, or between London and Berlin in Europe, or between Denver and Las Vegas in the US).

It makes a final crater about 230km in diameter, and 1.5 km deep. 8.3 seconds after impact , I get ignited by the blast of heat from the impact, which even at this distance is not unlike a nuclear blast – everything catches fire. If I’m still around after that, then around the 3 minute mark I feel the residual shaking from the 10.4 earthquake that the impact triggered (not enough to collapse buildings at my distance, but enough to be felt). Ejecta arrives at my location about 8 minutes after impact (a light dusting of millimetre-sized stuff with the occasional larger fragment). Then around the 50 minute mark (the heat is dying down at this point) I get deafened by the sound and any buildings still standing around me get blown away by the 1000 mph winds of the blast wave. If I crank down the impact velocity to a more reasonable 11 km/s then the heatblast is avoided and the crater is smaller, but the quake is still felt and the blastwave still does significant damage.

Either way, it’s not pretty :). And this is just from a comparatively tiny (relative to Earth) 10 km wide bit of nickel/iron. Thankfully there aren’t too many of those flying around on an earth-crossing orbit! It’s interesting to note that if this happened on a world without an atmosphere then the blast wave wouldn’t be an issue, and that’s what causes a lot the physical damage.

Though while I think it’s fine for smaller impacts, I’m not so sure about larger ones – I tried a 6000 km diameter object with a density of 5000 kg/m³ (i.e. about the same size and density as Earth) at 11 km/s and it made a 30,000 km diameter crater (so, about 3/4s of the Earth’s circumference) and yet it didn’t have any significant global effects other than to possible slow our rotation down? It really should result in the total eradication of everything on the surface, atmosphere blown away, probably the entire surface turned into a magma ocean, and the tilt maybe changing significantly (assuming the Earth doesn’t actually breaking apart due to the impact). So I’m not sure I’d trust it for really big impacts.

Though check out the pulldown list of possible impactors – there’s a surprise in there ;).