June 19th: Second Place Vesta

Date: June 19, 2010

Title: Second Place Vesta


Podcaster: The Ordinary Guy from Brains Matter podcast

Organization: Brains Matter – http://www.brainsmatter.com

Description: Who remembers second place? It’s a problem that plagues anyone who isn’t the biggest or fastest or shiniest. In today’s episode of 365 Days of Astronomy, we look at the second largest object in the Asteroid Belt – Vesta.

Bio: The Brains Matter podcast has been producing and communicating science stories and interviews since September 2006. The show is based out of Melbourne, Australia, and takes an everyday person’s perspective of science in easy-to-understand language.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by the Physics Department at Eastern Illinois University: “Caring faculty guiding students through teaching and research” at www.eiu.edu/~physics/.

Additional sponsorship for this episode of 365 Days of Astronomy is provided by Chuck McCorvey.


Hello everyone. I’m the Ordinary Guy – the host of the Brains Matter podcast, coming to you from Melbourne, Australia.

When you think of astronomy, you’re probably like me. I think of planets, moons, galaxies, black holes, comets… all those big or exciting things. What about asteroids? They tend to be the forgotten member of the astronomical family. They are usually quite benign, only occasionally causing a stir.

As you most likely know, there’s a rocky belt between Mars and Jupiter called the Asteroid Belt. Within the asteroid belt, there are a vast number of rocky objects called asteroids. The largest object in the Asteroid Belt is called Ceres – and as with everything else, people tend to remember first place. Bu who remembers who got a silver medal in a particular event at the last olympics? It’s the bane of second place, I guess.

What is the second largest object in the Asteroid Belt?

It’s an object called Vesta. It’s just over a quarter the size of Ceres, and measures, in round figures, about 580 km by 460 km, and has a mass of just under 2.7 x 10^20 kg. To put that in context, put 20 zeroes after a 3. A large person is in the order of about 1 with two zeros after it, in kilograms. As you can tell by the fact that the measurements are different in different dimensions, Vesta is not round.

You may recall that the IAU’s definition of a planet back in 2006 required an object to have ‘sufficient mass to assume hydrostatic equilibrium’ – in other words, nearly round. So does Vesta get classed as a Dwarf Planet? After all, Ceres is classed as one. Right now it’s not considered one, but this may change – in 2011, the Dawn spacecraft will orbit the asteroid, and astronomers will get a lot more data to make their determination at that point in time. The IAU draft proposal in 2006 listed Vesta as a candidate for a planet, incidentally. For the moment, the mass is less than what is required to be considered a Dwarf Planet by the IAU resolution XXXVI 5.

Let’s take a bit of a look back at the discovery of Vesta – it was discovered on the 29th of March, 1807 by a German astronomer by the name of Heinrich Wilhelm Olbers. It was named it after the Roman goddess of home and hearth, after Olbers allowed mathematician Carl Friedrich Guass to name the object.

When Ceres and Pallas were discovered in 1801 and 1802 respectively, Olbers proposed that both objects were the remains of a destroyed planet. He contacted Englishman William Herschel, suggesting a search in the area where the orbits of Ceres and Pallas intersected. He started his search that year, and he found Vesta a few years later.

Vesta was the fourth object to be found in the asteroid belt. For almost the next four decades, it, along with Ceres, Pallas, and Juno, were considered to be planets. So don’t fear Pluto, your demotion was definitely not a first!

So where abouts is Vesta? We’ve already established that the asteroid belt lies between Mars and Jupiter. The Earth lies at 1 AU, and Vesta lies at about 2.5AU. It rotates fairly quickly, even for an asteroid – we know the earth takes a day to rotate around its axis – Vesta takes 5.342 hours. There’s a range of temperature – from about -20 degrees when the sun is overhead, to about -190 degrees at the winter pole, although this varies depending on the seasons. And when I mentioned degrees, I’m referring to celsius! I could have said kelvin, but either way, real science people don’t use fahrenheit, right?

It’s believed that Vesta has a primarily a metallic iron-nickel core with a rocky mantle. Observations through the Hubble Space Telescope have shown that there’s a 460 km wide crater near the south pole – that’s 4/5th the diameter of the whole asteroid itself! The crater is so deep, that it exposes the subsurface of Vesta. There are several other craters on the surface, and some of the smaller solar system objects are thought to have been created by Vesta collisions. The Hubble has also showed that Vesta used to have lava flows, challenging the old views that asteroids were fairly dead, unexciting worlds.

Hopefully we’ll find out a bit more about Vesta thanks to the Dawn probe from NASA – this was launched on the 27th of September, 2007 and is the first mission to this particular asteroid. After sending back data on Vesta for about nine months, it’ll then move on to Ceres and study that, until it runs out of fuel. One of the big hopes of this mission is to figure out the precise mass of Vesta and this will then help astronomers figure out the masses of asteroids that are in turn affected by Vesta.

This is just a summary of some of the wonders of Vesta – if you’re interested in finding out more, I’d suggest you contact your nearest astronomy club, or do some research on it yourself – you’ll be amazed at what you find!

Thanks for listening everyone – and if you would like to hear more stories on science, curiosities and general knowledge, head over to www.brainsmatter.com.

Bye for now!

End of podcast:

365 Days of Astronomy
The 365 Days of Astronomy Podcast is produced by the Astrosphere New Media Association. Audio post-production by Preston Gibson. Bandwidth donated by libsyn.com and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. Until tomorrow…goodbye.


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