Vesta and Bennu

4 January 2019

NASA probe update: a couple of things are happening at the same time.

The New Horizons probe has just done its scheduled fly-by of Ultima Thule, and found that it looks like a 35 kilometre long bowling pin, spinning slowly in space. Ultima is way out, beyond the orbit of Pluto, and New Horizons is going pretty much flat out, over 50,000 km/h, with no way of stopping. It'll probably use its remaining fuel to change course so it can do a fly-by of another Kuiper Belt object.

At the same time, the OSIRIS-REx probe has gently settled into orbit around Bennu, an asteroid relatively close by - just beyond the orbit of Mars. This is the smallest object so far orbited by a probe, so orbiting is tough due to Bennu's incredibly small gravity. One wrong move and OSIRIS-REx will drift away into interplanetary space.

But when I think of planetoids (asteroids, Kuiper Belt objects, call them what you will) I tend to think of Vesta, the second-largest asteroid (after Ceres). This is probably because of Isaac Asimov's story "Marooned Off Vesta", which was his first published story, coming out in 1939.

Asimov was one of the main reasons I got into astronomy and science in general. And I think there's a pile of other ageing geeks out there in the same boat.

One of my challenges for 2019 is to take a photograph of Vesta. My own refractor, with its wide-angled 560mm focal length, will only get a dot which shifts position over two nights. However, a Cassegrain like a Celestron CPC 925 might just be able to make out a shape if we really (no, REALLY) stretch the optics with Barlows or other lenses.

Photo of Vesta: NASA