She’s a computational geophysicist whose computer models are intended to help figure out how to avoid the potential apocalypse of big comets or asteroids striking the Earth.
“It’s one of those things, like I keep a fire extinguisher in my kitchen,” Plesko says, “not because I expect to have a kitchen fire, but just in case, because sometimes kitchen fires happen.”
Right now, apparently, Earth has no extinguisher for asteroids.
Plesko and others from LANL were part of a group of scientists who held a news conference at the annual meeting of the American Geophysical Union last week in San Francisco that called attention to our planet’s unpreparedness for an asteroid strike.
“The biggest problem, basically, is there’s not a hell of a lot we can do about it at the moment,” said Joseph Nuth, a researcher with NASA’s Goddard Space Flight Center in Maryland.
“The point is,” Plesko said in an interview Tuesday, “it takes five years from the time NASA scientists get the money to the time they can launch something like OSIRIS-REx,” which was sent on its way in September to collect samples from the near-Earth asteroid Bennu.
How far out scientists on Earth can detect incoming asteroids is unpredictable, Plesko said.
“Some of them like Bennu (with a very low probability of striking the Earth), we have 200 years of warning,” she said. “Some of them, like the comet Siding Spring that almost hit Mars in 2013, we had just six months warning before that got close to Mars.”
“And if that had been close to Earth, which is not a big change in its trajectory,” she continued, “… We would have been caught really short-sheeted there, because we would have not had a spacecraft ready to go. We would have not had time to prepare for it.”
Plesko’s experience at the Los Alamos lab started as a summer student in 1998 as she was working on her doctorate at the University of California at Santa Cruz. She moved to Los Alamos 10 years ago and has been on staff since 2011.
Plesko seems to have heard a lot of jokes about whether she’s just playing an advanced version of “Space Invaders” with her asteroid-avoidance models developed on LANL’s supercomputers.
“Yeah, my mom teases me about that all the time,” she said when a reference was made to the old arcade game during her interview with the Journal.
The ‘kinetic impactor’ option
So, wouldn’t earthlings just try to blow up an approaching space rock? Not necessarily, said Plesko.
“There are scenarios where it might be better to blow it up, what we call disrupt and disperse the object,” she acknowledged.
“But for the most part it takes less energy to change the orbit than to blow it to smithereens and push the pieces away from Earth’s orbit. It’s just a simpler process, at least according to the numerical models we’re working on.”
One way to bump an asteroid off track is to use a “kinetic impactor, which is essentially a big space cannonball,” Plesko said. The modeling work at LANL is trying to answer questions like “how big of an impactor do you need, when do you need to hit it, how will different objects respond.”
These cannonballs would be sizeable – hundreds of metric tons (a metric tons equals 2,205 pounds). For a big asteroid, it would probably take as many as six or seven rockets to deliver enough cannonballs. “That’s really straining the launch capabilities of the United States,” Plesko said.
A nuclear device would be easier to launch. She said there are safety and security issues around nukes. “But that’s part of the goal – let’s think this thing through carefully, while the heat is not on.”
NASA and the European Space Agency are working on a project, with a launch expected in 2020, to send a kinetic impactor to the asteroid Didymos, which is about 800 meters across and has a “moonlet” 150 meters across that revolves around the bigger object. NASA’s Double Asteroid Redirection Test (DART) spacecraft will act as an impactor to try to change the orbit of the moonlet.
“The cool thing there,” Plesko said, is that without changing the dual-asteroid system’s orbit around the sun or nudging it toward Earth, “we test all the physics by testing the orbit of the little guy around the big guy.”
“It’s a baby step,” she said. “It’s the first proof of concept.” Developing a spacecraft for “a real deflection of a larger object, that’s going to take some homework, that’s going to take years to develop,” Plesko said.
The lead time for dealing with an incoming asteroid, as well as the composition of the object, would be crucial in determining how to attack it.
“If you have, say, 10 years, you only need to speed up or slow down the object by a centimeter per second before it will completely miss, 10 years later, its intercept with Earth,” she said. “Now, if you have a year, of course, you have to speed it up a lot. And you have to push on it harder. That makes it more likely that you need a larger amount of energy. And of course, the largest amount of energy that we can put on a spacecraft and deliver somewhere like that is a nuclear device.”
Are we due?
Whether Earth is due for a big impact from a space object is “a complicated question,” Plesko said.
Stuff is falling on the Earth all the time – small pieces with a total mass about equal to that a Volkswagen Beetle come down every day, she said. The Chelyabinsk meteor that hit Russia in 2013 and caused widespread damage and injury served as a reminder “that there are larger things out there that come in less frequently.”
“When you think about the really big things, for example the KPG impact that killed the dinosaurs, one like that happens, we think, every 65 million to 100 million years,” she said. And KPG hit, well, about 65 million years ago. Still, that 35-million-year window estimated for the next giant impact is pretty wide, she noted, adding, “So I’m not worried about it.”
That’s no reason to procrastinate, she said.
“You don’t want to do all your homework the day before your final,” she said. “You want to do your homework spread out throughout the quarter and not at the last minute, because you’re going to do better, No. 1, and you’re going to get it all done.
“So that’s what Joe (Nuth) is talking about – while there’s not an urgent threat of anything coming at us, let’s get our homework done first, while we have time to test things carefully and think them through and do the design right.
“That way if, God forbid, something came at us, we would have a spacecraft ready to go, on the shelf.”