In 2004, US astronomers found an inconspicuous spot in the sky: it’s a new asteroid, which in itself is not unusual. But this asteroid is special: initial calculations show that there is a 2.7 percent probability that it could fall to earth in April 2029. The all-clear came two years later, thanks to more detailed observations. The 350-meter-wide asteroid, now named Apophis, will miss Earth, albeit just barely.
“Apophis will pass Earth in geostationary orbit at 30,000 kilometers. You will be able to observe it, for example from the Middle East or from Eastern Europe. It’s going to be relatively bright, which means you can just about see it with the naked eye or with binoculars,” says Vishnu Reddy, one of the participants at the Apophis T minus seven years conference.
Could small objects slip through the observation network?
Although the impact is now considered impossible, astronomers have prepared for the event with simulation games. Reddy is one of a group of 100 researchers worldwide who are now discussing for the third time how Earth could detect and ward off potentially dangerous asteroids. The result: Only if existing search telescopes continue to be sufficiently funded is there a chance of discovering smaller chunks.
“We have tools and techniques to detect celestial bodies the size of Apophis. The smaller objects are challenging. A 140 meter asteroid can destroy large parts of a country or wipe out a small country entirely. We have to find these chunks! And then we need to study them in enough detail to calculate their orbits a hundred years into the future.”
OSIRIS-REx on a flying visit
While large parts of asteroids in the 300-meter class of Apophis are known today, astronomers only know an estimated ten percent of all objects that are only half that size. In order to better understand the mechanical properties of such asteroids in the event of an emergency, NASA would like to observe Apophis directly during its flyby in 2029: The US space agency will send the OSIRIS-REx space probe to Apophis, which is still on its way back from another asteroid.
Michael Nolan leads the mission’s science team: “We’re rarely able to experiment with something this big. Above all, we want to understand how sunlight changes the asteroid. It could be that the surface will be exposed a bit as it flies by. While we don’t think Apepa’s shape will change dramatically, small landslides could occur.”
What countermeasures might work?
The spacecraft is scheduled to reach Apophis after three swing maneuvers on Earth in April 2029, shortly after its close flyby. OSIRIS-REx is designed to take pictures and possibly dig on the surface with the robotic arm to answer an important question: How strong is the material? How would an asteroid like Apophis react if explosives or, in an emergency, nuclear weapons were detonated on it? These questions are still open.
Michael Nolan: “As far as we know today, we would have to be extremely careful because we don’t yet understand asteroids well enough. Once we have studied them more closely, one day we might be able to distract them with simple, non-violent measures.”
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