BAN #319: Snowy mountains, Meteorites from Vesta

3 May 2021   Issue #319

[The planetary nebula M 2-9, winds from a dying star. Credit: NASA / ESA / Hubble Legacy Archive / Judy Schmidt]

Subscribers flash across the sky and sometimes rain down rocks. Though I might be thinking of meteoroids.


Because my home state is pretty

Late spring in Colorado is a mess. Warm one day, freezing the next, rain, snow, sometimes both… but it does have its perqs.

[Credit: Phil Plait]

That’s Mount Meeker (left) in front of Longs Peak (right), the two tallest mountains in Rocky Mountain National Park, and visible for a long, long way. Most of the year they’re brown and maybe green, but for a few days they sparkle white with snow. The Sun takes care of that pretty quickly, but for just this short time it’s nice to appreciate them this way.

If you want to see a higher-res version, I put it on my Flickr site.

Blog Jam

What I’ve recently written on the blog, ICYMI

[3D models of the Crab Nebula generated from spectra: The view as we see it from Earth (left) versus from a different angle, where the heart shape becomes more apparent. From Tuesday’s article. Credit: Thomas Martin, Danny Milisavljevic and Laurent Drissen ]

Monday 26 April, 2021: For its birthday, Hubble has cake with several octillion tons of flaming candles on it

Tuesday 27 April, 2021: The 3D heart of the Crab Nebula

Wednesday 28 April, 2021: A star that lived, then died, then lived again, then died for real

Thursday 29 April, 2021: Dating craters: Wolfe Creek is younger, Meteor Crater older, than previously thought

Friday 30 April, 2021: Hubble sees a nearby very young planet finishing up a growth spurt

Astro Tidbit

A brief synopsis of some interesting astronomy/science news

Here’s something cool: Did you know that some meteorites found on Earth can be traced back to their parent asteroid? It’s true. It’s not easy, usually, but in some cases there’s enough evidence to be pretty sure.

Stony meteorites fall to Earth all the time, and most come from asteroids. Asteroids sometimes impact each other, and when they do eject shrapnel into space. Sometimes these are quite large, asteroids in their own right. They tend to stay on similar orbits, and we call these asteroid families. In some cases, spectra taken of the asteroids can be used to ID minerals in them, and show they have a common origin.

The same can be true for meteorites, where their compositions can be ascertained extremely well since they can be analyzed in a lab. As it happens, quite a few meteorites have been tied to the giant asteroid Vesta*; I described this in a blog post back when I wrote for Slate. I even saw such a meteorite at SpaceFest IX a few years back:

So. In 2018 a small 1-meter asteroid was discovered just hours before it impacted Earth. Called 2018 LA, it broke up in Earth’s atmosphere over Botswana. Small ones like this tend to completely fall apart, but some small meteorites can land. Scientists immediately set out to search for them, and found quite a few. Subsequent testing showed them to be in the same mineral group as Vesta.

I’d give more details on the hunt, but the SETI Institute already has a great article about that. There’s a good news article from Canada’s Western University about this, too, and the scientist who led the search, Peter Jenniskens, has a poster presentation online you can take a look at for more tech details.

[One of the fragments of 2018 LA found in Botswana. I’m guessing it’s roughly a centimeter in size. Credit: SETI Institute]

I love all the moving parts to this, all the pieces that fit together to ID these meteorites. One thing I found interesting is that the orbit for 2018 LA could be found, since there were enough images of it from when it was still in space (and it was tracked as it burned up) to be able to backtrack it. It came from the inner asteroid belt, about 300 million km from the Sun. That’s interesting, because an asteroid orbiting there goes around the Sun four time for every once Jupiter does, what we call a resonance. This means Jupiter’s gravity can yank asteroids out of such orbits, tossing them inward toward the Sun.

That’s why it was able to get to Earth. Also, Vesta’s orbit is a little bit outside of this resonance but still in the inner belt, so that fits as well.

And there’s more! We’ve been to Vesta; the Dawn probe orbited Vesta for over a year, mapping it in great detail. It found several relatively young (~20 million year old) craters on it, and these may have been the impact sites that created its families and various meteorites found on Earth.

Between all that and the mineralogical study, it’s pretty clear the 2018 LA asteroid was once part of Vesta. Isn’t that awesome? It’s ironic: We get pieces of asteroids sent to Earth for free, but sometimes you have to go to those asteroids to figure out what else you need to understand them. But together these provide powerful evidence of the origin and sometimes even the history of the meteorite.

* In fact most planetary scientists consider Vesta to be a protoplanet, and not an asteroid; a body so large it was on its way to becoming a proper planet before it ran out of material to grow with.

Et alia

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