Jump to content
Sign in to follow this  
JohnD

I'm a scientist, me!

Recommended Posts

The OSIRIS REx space probe is now in orbit around the asteroid Bennu.   Bennu is a 'near-Earth' asteroid, that orbits the Sun betwen the Earth and Mars.   It is on the medium risk list of asteroids that could impact us, and in 2060 will pass within  half a million miles of the Earth, a near miss in astronomical terms!       The mission plan is to collect a sample of the surface and return it to Earth, but Benu appears to the  "rockpile" object, a collection of small boulders 265 miles across, held together by their mutual gravity.    The surface is chaotic, so that landing to collect a sample will be hazardous.    Nasa is asking 'citizen scientists', you and me, to help them map the surface of Bennu, so that they can select the safest touch-down point.

This is what Bennu's surface looks like:

See Explanation.  Clicking on the picture will download  the highest resolution version available.

For scale, the pale boulder top right is about 4 meters high, so many of these are big enough to tip a spacecraft over as it tries to land.

If you go to https://bennu.cosmoquest.org/ and register, you will be shown close-up pics of Bennu's surface, and asked to mark the boulders - there is a simple tutorial to show you how.   

Less exciting than Grand Theft Auto, but a lot more valuable!

JOhn

Edited by JohnD

Share this post


Link to post
Share on other sites

NASA will know that gravity pulls in all directions, not just our familiar downwards. So choosing a flat valley bottom might not be a good idea as the craft will be pulled sideways by surrounding hills. That happens on earth too and is taken into account in predicitng sea level rise eg. Greenland ice exerts a sideways pull on north Atlantic, so if the icecap melts the nearby sea level will nto rise as mcuh as predicted by meltwater alone, and might fall.

So my suggestion is to look for a flat hilltop on Benno.

Peter

Share this post


Link to post
Share on other sites

The surface gravity on Bennu (the name was given in a competition run by the Planetary Society, won by Micheal Puzio, aged 9) is 0.01g.     The effect, even in a steep sided valley would be a tiny fraction of that.    The Schiehallion Experiment of 1774 sought to measure the gravitation of that mountain in Scotland, to confirm Newton's Laws.    Maskelyn found that a hanging mass was deflected from the vertical by 10 seconds of angle.  at 60 minutes to the degree and 60 seconds to the minute that is 0.003 of a degree.  Schiehallion is a thousand meters high, a cone a bit wider at the base.     There are a few very large rocks sticking out of the surface, easily avoided, that might have a similar effect in making the gravity field around Bennu assymetric, but otherwise just a remarkably regular rhomboid section.

NASA are more concerned to find a landing point that will not tip the probe over as it comes down.    Rather like Apollo 11, but without a pilot aboard to steer it clear.

John

Edited by JohnD

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×
×
  • Create New...