A 73bn-kg, skyscraper-size chocolate creme egg spinning fast enough to eventually explode – it's asteroid Bennu
- Reference: 1602219731
- News link: https://www.theregister.co.uk/2020/10/09/bennu_core_nasa/
- Source link:
“You could imagine maybe in a million years or less the whole thing flying apart,” [1]said Daniel Scheeres, coauthor of a study [2]published in Science Advances on Thursday into the cosmic rock. Scheeres and a large team of astronomers studied the asteroid using data gathered from OSIRIS-REx, a spacecraft launched by NASA that is expected to retrieve a sample of the space rock’s surface on [3]October 20 .
The trick to probing the hidden interior of Bennu was to measure its gravity field. Scientists mapped this out by measuring the gravitational pull exerted on the [4]OSIRIS-REx as the probe orbited the asteroid, and modelling the [5]tiny pebble-sized bits of dirt being flung from the space boulder's surface and placed into temporary orbits around the thing.
[6]Previous measurements allowed researchers to estimate the size and mass of Bennu; it’s about as tall as the Empire State Building, and a whopping 73 billion kilograms.
This latest analysis looked deeper into the asteroid, and found it was less dense inside compared to outside. Bennu is essentially a giant mound of debris held together in a spinning-top shape. Its exterior is hard and rugged while the rocks in its interior are loose and less tightly packed. What’s most concerning is that it’s softest at its very core, and its equator bulges out.
Shine on you crazy diamond: We don't know who needs to hear it but NASA's explained the weird shape of the Bennu asteroid [7]READ MORE
“If you can measure the gravity field with enough precision, that places hard constraints on where the mass is located, even if you can’t see it directly,” said Andrew French, a coauthor of this latest study and a scientist at NASA’s Jet Propulsion Laboratory. Like all celestial bodies in the Solar System, Bennu’s motion is affected by the Sun. Its surface is warmed by solar rays, and some of that heat is absorbed and re-emitted into space. The photons leaving the asteroid act like a kick, causing it to spin.
The phenomenon is described as the Yarkovsky–O'Keefe–Radzievskii–Paddack effect, or [8]the YORP effect for short. A previous study found that Bennu’s spin rate appeared to be accelerating over time, threatening to tear it apart.
“When you spin this guy up, you create a competition between the gravity that’s holding you down and the centrifugal acceleration, which is trying to throw you off,” said Scheeres. “If its core has a low density, it’s going to be easier to pull the entire asteroid apart.”
But don’t worry, it may take over a million years for Bennu to spin itself into a destructive frenzy. It’ll stick around long enough for NASA’s OSIRIS-REx probe to retrieve a regolith sample, and for many other spacecraft to study it in more detail.
“We were hoping to find out what happened to this asteroid over time, which can give us better insight into how all of these small asteroids are changing over millions, hundreds of millions or even billions of years,” Scheeres said. “Our findings exceeded our expectations.” ®
Get our [9]Tech Resources
[1] https://www.colorado.edu/today/2020/10/08/scientists-peer-inside-asteroid
[2] https://advances.sciencemag.org/content/6/41/eabc3350
[3] https://www.theregister.com/2020/09/25/bennu_asteroid_sample/
[4] https://www.asteroidmission.org/objectives/
[5] https://www.theregister.com/2020/09/10/bennu_asteroid_nasa/
[6] https://www.colorado.edu/today/2019/03/19/osiris-rex-spies-weird-wild-gravity-asteroid
[7] https://www.theregister.com/2020/09/10/bennu_asteroid_nasa/
[8] https://www.planetary.org/articles/20141211-the-yorp-effect-and-bennu
[9] https://whitepapers.theregister.com/
Re: How common is this?
I've added a link to an in-depth explanation of YORP by the probe's principal investigator. As you can see it goes on for quite a while, and in all honesty, we ran out of time to condense the effect's description down into an explanation that would satisfy everyone.
Like any product, you have to draw a line at some point and ship it. Articles are no different -- otherwise, nothing would get published because we'd forever be trying to improve or add to them.
I encourage you to read up on it and share here your best explanations of it.
C.
Re: How common is this?
Objects can spin up or down from this effect, but it has negligible impact on large bodies because the amount of mass to be shifted increases with r-cubed whereas the surface area increases as r-squared. Also, larger bodies tend to have a less irregular shape.
Re: How common is this?
Could the YORP effect be used to power a self-turning doner kebab grill or spit-roast?
If I'm going to build one I guess I'll need a bigger heater, a colder atmosphere, and bearings with less friction than Disaster Area's stuntship, for starters.
What else will I need?
Re: How common is this?
"What else will I need?"
Some yood quality Halal Doner meat, the extra hot chili sauce and some crisp salad.
Re: How common is this?
A yood quality elephant leg?
Re: How common is this?
A very long piece of paper to write down all the other things you'll need...
73 billion kg of chocolate creme egg? I hope OSIRIS-REx brings back enough to share and doesn't melt it on re-entry.
"73 billion kg of chocolate creme egg"
Ah, an example dating from before Cadbury's resizing exercise.
Was there ever....
... a time before the Cadbury re-sizing exercise? I thought that it had been going on since the beginning of time.
Re: Was there ever....
Cadbury creme eggs were unchanged for decades, as was Terry's chocolate orange.
The chocolypse (Kraft buyouts of Cadbury & Terry's) ruined them.
Sooga! Sooga! Sooga!
That's no moon....
It's a mudhorn egg!
A new Register measure of mass - the Bennu?
Interesting thought
Surely the fact that one of the first few asteroids that we have inspected up close is apparently close (in geological terms) to disruption has important implications.
It implies that it is common for such bodies to be close to being disrupted, and hence places limits on the expected life-span of such bodies. Therefore, it also implies that such bodies must form at a rate to replace the loss by disruption. By form, I include entry into the inner solar system by perturbation of the Oort cloud.
Re: Interesting thought
Isn’t the Oort Cloud a bit far from the Sun for major YORP effects? Whereas Bennu is much closer in.
How common is this?
It seems like any object with some rotation perpendicular to its orbit would slowly spin up. More explanation of the YORP effect would have been helpful, especially why it prefers to spin an object up rather than down. I infer that the time in sunlight makes the sunset side of the asteroid hotter than the sunrise side so more heat energy is radiated.