EXCERPT: Physics is having a moment. Almost two years ago, the world stopped in awe as the Philae lander became the first module in history to soft-land on a comet. The recent discovery of gravitational waves has also made ground-breaking progress in the work Albert Einstein began a century ago. And, most recently, NASA has announced its plans to send a mission to Bennu: a 500m long, rotating cluster of dust and rock which swings into sight of Earth every six years. The mission requires an investment of one billion US dollars and will take seven years from its launch to return. So what makes Bennu worthy of a place in the canon of recent scientific breakthroughs...
EXCERPT: A swarm of 10,000 or more black holes may be orbiting the Milky Way's supermassive black hole, according to observations from NASA's Chandra X-ray Observatory in 2015. This would represent the highest concentration of black holes anywhere in the Galaxy. These relatively small, stellar-mass black holes, along with neutron stars, appear to have migrated into the Galactic Center over the course of several billion years....
...And, most recently, NASA has announced its plans to send a mission to Bennu: a 500m long, rotating cluster of dust and rock which swings into sight of Earth every six years.
The American Osirisrex spacecraft has arrived at Bennu, which looks just like similarly small (1 km, about twice as big) Ryugu, where a Japanese spacecraft currently is.
This little animated gif (from NASA) consists of telescopic photos taken about one-a-day since the middle of October, as Osirisrex approached little Bennu. (A microworld!) The last photo is from about 200 miles away.
I'm speculating that if these little objects with microscopic gravity are rotating, centrifugal 'force' gives them equatorial ridges. So maybe this oblate-spheroid shape is characteristic of very small rotating bodies.
YazataDec 31, 2018 06:32 PM (This post was last modified: Jan 1, 2019 04:34 AM by Yazata.)
While everyone is paying attention to New Horizons' arrival at Kuiper Belt object Ultima Thule, Osiris Rex will be completing a very delicate thruster burn lasting a few seconds that put it into a gravitational orbit of tiny Bennu (only 500 meters across). It's going to be the smallest object that a spacecraft has ever orbited.
While orbital velocity on Earth is about 18,000 mph, Osiris Rex will be orbiting Bennu at the blistering pace of 0.13 mph (6 cm/sec), relative to Bennu.
New Horizons will be passing Ultima Thule at 32,212 mph, relative to Ultima Thule.
It's interesting that Ultima Thule is far enough away, about 6 light-hours, that relativistic effects become relevant. Timing for the spacecraft commands is 'SCET' time, 'Spacecraft Event Time', time relative to the New Horizons vehicle itself according to the vehicle's own on-board clock.
Edit: Osiris Rex has completed its thruster firing and has gone into in orbit around Bennu.
Jonathan McDowell reports that the dimensions of Osiris Rex's orbit is a whopping 1.5 by 2.0 kilometers! So not only is this the smallest object ever orbited, it's the closest that an orbiter has ever been to object it's orbiting.
It's kind of amazing that an object only 500 meters in diameter can still have a useful gravitational field that permits an object to orbit it.
So this New Years Eve is a big night for NASA. Two records. Both the smallest object ever to receive an orbiting satellite, and the farthest object ever to receive a reconnaissance fly-by.
Bennu is spitting material into space! That caught the Osiris Rex team by surprise.
Maybe the distinction between asteroids and comets isn't as clear as once assumed. Apparently there's some kind of volatile material on Bennu that's being heated by the sun and turning into vapor, mini-explosively, enough to propel small rocks off. (Bennu's so small that it has almost no gravity.) It's a pretty weak comet tail, but there it is.
YazataApr 14, 2020 08:54 PM (This post was last modified: Apr 14, 2020 09:25 PM by Yazata.)
We may have forgotten about it, but Osiris Rex is still up there at Bennu (since 2018)!
The plan is to land Osiris Rex on the asteroid in August to collect samples for return to Earth.
Today, April 14, the spacecraft and its NASA controllers are practicing the maneuvers necessary to do that. The microgravity makes that a non-trivial thing, the vehicle has to move very gently. It's also 13 light minutes away, so the vehicle is behaving autonomously and commands can't be in real-time. It will approach very close to the asteroid, then move away again. (All while much of the team works from home and the rest maintain social distancing.)
I don't know of any live-feed. Updates are appearing pretty continuously on twitter here:
YazataApr 16, 2020 03:23 AM (This post was last modified: Apr 16, 2020 03:47 AM by Yazata.)
Here's something that Osiris Rex filmed last night as it approached and then retreated from Bennu. They say that the closest it got last night was 65 meters away (~213 feet).
C COct 10, 2020 06:10 AM (This post was last modified: Oct 10, 2020 07:01 PM by C C.)
Asteroid Bennu was once part of a space rock with flowing water: The asteroid Bennu is a strange little place, but data from NASA’s OSIRIS-REx mission is starting to unravel its mysteries. The spacecraft, which has been orbiting Bennu since December 2018, is gearing up to take a sample from the asteroid’s surface later this month. In preparation, it has gathered a smorgasbord of information, including hints that Bennu’s parent asteroid may have had flowing water.
Bennu is a type of asteroid called a rubble pile, formed when something smashed into a larger asteroid billions of years ago and the bits coalesced into many smaller asteroids. By studying Bennu, which is about 500 metres wide, we can learn more about this parent asteroid, which was probably a few hundred kilometres across... (MORE)
Ancient asteroid Bennu contains ingredients for life: . . . When Bennu’s parent body was still young, it had enough heat to keep liquid water in its soils. As this water dribbled through the asteroid, it slowly deposited carbonate minerals within the fractures it passed through. Later, when gravity sculpted Bennu from the parent body’s debris, some of these primordial mineral veins survived intact, within boulders now strewn on Bennu’s surface.
The largest of these carbonate veins seen so far stretches more than three feet long. The veins’ width and size imply that for thousands—if not millions—of years, Bennu’s parent body had a sizable amount of hydrothermal activity.
“This is why we do spacecraft exploration,” says OSIRIS-REx team member and study co-author Hannah Kaplan, a planetary scientist at NASA’s Goddard Space Flight Center. “We didn’t expect to see these things, we cannot see them from Earth, and we needed to be orbiting pretty close up to the asteroid in order to see them.” (MORE - details)