Samstag, 3. Oktober 2015 - 22:30 Uhr
The odds of you personally getting killed by an asteroid are not that high: About 1 in 75,000 seems to be a reasonably accurate number based on available data. The thing about asteroids, though, is that while it’s very unlikely that Earth is going to be hit by one capable of doing significant damage, if it does happen, it’s going to trigger bad times for a lot of people—millions, if not billions. That 1 in 75,000 means that you're almost twice as likely to die from a globally destructive asteroid impact as you are from either an earthquake or a lightning strike.
Does this mean we should panic? I mean, sure, go ahead, if you’ll feel better afterwards. But really, what it means is this: if we can agree that it makes sense to allocate resources towards reducing the risk of people getting killed by things in proportion to the likelihood of those things actually occuring, then asteroid detection and intervention is definitely worth our attention. Probably more so than some other things. Like terrorism. But I digress.
The European Space Agency and NASA have a good understanding of the importance of finding and (hopefully) avoiding asteroids, and they’re joining forces on an Asteroid Impact & Deflection Assessment mission called AIDA. The objective of this mission is awesome: to slam a spacecraft into an asteroid with as much force as possible, and see what happens.
As you may remember, this is not the first time that we’ve deliberately crashed a spacecraft into an asteroid just to see what would happen. In 2005, the Deep Impact spacecraft launched a 370-kilogram copper-cored impact vehicle at the 6-km-wide comet Tempel-1, and then hung back to watch the show.
That impact changed the orbit of the comet by something like 10 centimeters. Not much, obviously, but it’s a start.
The AIDA mission has a similar structure to Deep Impact. It has two primary components: an observatory called AIM (Asteroid Impact Mission) being developed by ESA, and an impactor called DART (Double Asteroid Redirection Test) being developed by NASA. The AIM observatory, which will be launched first, won't be hugely complicated or expensive. It's expected to carry some cameras and radar and communications gear and stuff like that, and also a boxy little lander based on DLR’s MASCOT. There will be room for a few cubesats, too.
AIM will launch out towards a near-Earth asteroid called Didymos. Didymos was chosen because it's super easy to reach from Earth, and at about 800 meters in diameter, it’s the size of something that we'd probably want to try and avoid. Didymos also has a little moon (technically, it’s a binary asteroid) which has a diameter of 150 m. The moon, known as Didymoon, is going to be the target asteroid, because any change in its orbit will be easier to measure, and it’s actually more effective to move the moon, and then let the moon’s new orbit shift the orbit of the binary system as a whole.
NASA will be sending DART on a much more direct course since it won't have to sneak into orbit around Didymos. Instead, it’ll smack into Didymoon at just over 6 kilometers per second (13,400 miles per hour), abruptly converting most of its roughly 300 kg of mass into a stupendous amount of energy. The hope is that when all the dust settles, AIM will be able to measure a change in Didymoon’s orbital velocity of about half a millimeter per second. Given enough time, even that minuscule a shift could be signficant.
You don’t have to worry about this tinkering with Didymos’ orbit, though. As NASA points out, “it is important to note that the target Didymos is not an Earth-crossing asteroid, and there is no possibility that the DART deflection experiment would create an impact hazard.” Good to hear. If everything runs on schedule, AIM will launch in 2020, and the DART impact will happen in 2022.
This direct approach is just one way that we might be able to deflect an asteroid from Earth impact; NASA is going to try a gravity tractor in 2020, for example. If (when) we need to put these techniques into practice, the one we choose will depend on how long we have before impact, the size of the asteroid, where it is, what it’s made of, and all kinds of other factors that we can’t know in advance. All we can do is experiment and practice, because when the time comes, a failure of the technologies that NASA, ESA, and others are developing could mean anything from the obliteration of an entire city to the collapse of civilization, to the total extinction of the human race.
Quelle: IEEE Spectrum
AIDA DOUBLE MISSION TO DIVERT DIDYMOS ASTEROID’S DIDYMOON
AIM arriving at Didymos
An ambitious joint US-European mission, called AIDA, is being planned to divert the orbit of a binary asteroid’s small moon, as well as to give us new insights into the structure of asteroids. A pair of spacecraft, the ESA-led Asteroid Impact Mission (AIM) and NASA-led Double Asteroid Redirection Test (DART), will rendezvous with the Didymos asteroid and its small natural satellite, known informally as ‘Didymoon’. Following a period of study of both asteroids and detailed mapping of Didymoon by AIM, DART will impact with Didymoon and AIM will assess the mission’s effectiveness in diverting the moon’s orbit around Didymos. The AIDA mission is being discussed today at the European Planetary Science Congress (EPSC) 2015 in Nantes, France.
Patrick Michel, the lead of the AIM Investigation Team, said, “To protect Earth from potentially hazardous impacts, we need to understand asteroids much better – what they are made of, their structure, origins and how they respond to collisions. AIDA will be the first mission to study an asteroid binary system, as well as the first to test whether we can deflect an asteroid through an impact with a spacecraft. The European part of the mission, AIM, will study the structure of Didymoon and the orbit and rotation of the binary system, providing clues to its origin and evolution. Asteroids represent different stages in the rocky road to planetary formation, so offer fascinating snapshots into the Solar System’s history.”
AIM is due for launch in October 2020 and rendezvous with the binary system (65803) Didymos in May 2022. Binary systems make up around 15% of the asteroid population. Egg- shaped Didymoon (about 160 metres in diameter) orbits the diamond-shaped Didymos asteroid (about 750 metres in diameter) every 12 hours at an altitude of 1.1 kilometres. Ground-based observations show that Didymos is probably a common ‘chondrite’, or stony asteroid formed of dust from the primitive solar system. At present, Didymoon’s mass and density are unknown.
AIM will measure Didymoon’s mass shape, density and dynamic properties and map the asteroid’s surface at visible and infrared wavelengths, as well as using radar to probe
beneath the surface. It will deploy a small lander, MASCOT-2 (built by the German aeronautics and space research centre, DLR), in order to transmit and receive radio signals through Didymoon to investigate the internal structure. In October 2022, AIM will move to a safe distance to observed DART’s impact with Didymoon and analyse the plume of material ejected. It will then resume its mapping and monitoring mission to study internal material revealed in the crater and any changes to Didymoon’s orbit.
Recent missions have shown that asteroids are extraordinarily diverse in their geology, structure and evolution. All asteroids appear to be covered by soil, or ‘regolith’, but this varies from fine grains to lumpy pebbles. Density measurements show that most asteroids are aggregates of material, rather than solid bodies, but it’s not clear whether they are filled with large rocks and pockets of empty space, or gravel. The combination of AIM and DART will give new insights into the relationship between an asteroid’s surface and its interior, and new understanding of how asteroids and binary systems form.
AIM will also deploy three cubesat to assist with observations and to test new science and technology capabilities, including intersatellite communications links in deep space.
ESA’s Project Scientist for the AIDA/AIM mission, Dr Michael Küppers, said, “As well as fascinating science, AIDA offers a unique opportunity to demonstrate new technologies for ESA. AIM will deploy MASCOT-2, the ESA’s first lander since Philae, and will test operations that will give valuable experience for future Mars sample return missions and human exploration.”