“Vermin of the Skies”
The JPL scientist in charge of tracking incoming asteroids tells us if we should be worried.
- By Heather Goss
- AirSpaceMag.com, February 05, 2013
Courtesy Don Yeomans
(Page 2 of 3)
How do you make that calculation? If you’ve found approximately 40% of the near-Earth asteroids 140 meters and bigger, how do you know what the total number is in order to get a percentage?
It’s all done statistically. If our NASA-supported telescopes are searching every night for new near-Earth objects, let’s say over a ten-year period they find 900 objects larger than a kilometer. At the end of that ten-year period, it turns out that for every 10 objects they find, nine of them have already been discovered. Then you would say, alright, we’re at a point where we’ve found 90 percent of the population already, and if we’ve found 900 of them, the total population is likely to be 1000.
What is the best way to find near-Earth asteroids?
The ground-based optical observations are finding a lot of these objects. On the other hand, if you’re asking what way would be most efficient, then you would need a near-infrared telescope in space. Because these asteroids are dark, they absorb sunlight and radiate heat, mostly in the infrared, so they’re much easier to see in the infrared than in the optical. Ideally you’d like to have an infrared detector at the back end of a good-sized telescope, in either Earth orbit or one that’s not too dissimilar to the orbit of Venus. That’s the [B612 Foundation] Sentinel approach, and that would be the ideal technique for finding these objects.
A newly discovered object, Comet ISON, has been in the news lately, and it sounds like we’ll be able to see it bright in the sky this fall.
It was found by a couple of Russians at an observatory, International Scientific Optical Network, that’s what the name ISON stands for. This comet is already fairly bright and its out near Jupiter, so if we extrapolate its brightness as it comes in very close to the sun on Thanksgiving Day of this year, it has the potential to be very bright in the morning sky, or actually in the evening sky after sunset. Having said that, I’m old enough to remember Comet Kohoutek back in 1973; we predicted that would be the comet of the century and it turned out to be a bit of a fizzle. Comet brightness and behaviors are notoriously difficult to predict. But, if this comet behaves itself and acts like most comets it will put on a pretty good celestial show come this November.
What seems interesting, and tying it back to your book, is that they only just found it a few months ago. There are still these surprises out there in the sky, so this comet seems like a good argument for why we need to keep looking all the time.
That’s true. Comets, some of them get cut from the Oort cloud, which is at the very limit of our solar system, at 100,000 times the distance between the sun and the Earth. It takes millions of years for those objects to get from the Oort cloud to the inner solar system. ISON is a comet from the Oort cloud, so it’s almost certainly on its first return to the inner solar system. It’s scientifically interesting because it really hasn’t evolved much; it’s been out in the deep freeze of this Oort cloud for so long, retaining the percentage of ices and dust that formed some 4.6 billion years ago. With comets that have been around the sun several times, like Halley or other periodic comets, the volatile ices like carbon monoxide or carbon dioxide usually get depleted, and you’re left pretty much just with water ice. But these new [comets], they come in with their entire suite of volatiles – carbon monoxide, carbon dioxide, methane, ammonia, water – and so they’re the ones that are really the most interesting. I think that’s why astronomers are particularly excited about this comet.
Going back to potentially dangerous near-Earth objects, you write that we’ve started to look for these at the same time that, thankfully, we’ve developed the kind of technologies that could save us should we find one coming our direction. How might we be able to save ourselves from impact?
The key is: find them early, find them early, and find them early. If you find them 10, 20, 30 years prior to a predicted Earth impact, then you do have time to deal with them. So let’s say we find an object that’s 100 meters in diameter that’s predicted to hit the Earth 20 years down the road, then the easiest and simplest [solution] would be to simply run into it with a spacecraft. We demonstrated the navigational technology to do that when the Deep Impact mission purposely ran into Temple 1 on July 4, 2005. Just run into it, slow it down a millimeter per second or two, change its orbital period so that in 20 years time when it was predicted to hit the Earth it would miss by a wide margin. There have been other techniques discussed, everything from a so-called gravity tractor, which is just too wimpy to be a primary deflection device, to paintballs which is cute and colorful, but just nonsense.
Is that the method of putting paint on one side in order to change its reflectiveness, and that would sort of push it a little bit in some direction?
It would change the orbital dynamics of the object just a little tiny bit, but it’s really just ridiculous. I would take the spacecraft carrying these paintballs and run the entire spacecraft into the asteroid [laughs]. There are some other techniques – a solar reflector, a solar sail, laser ablation techniques – but some of these are far more complex, require far more sophisticated engineering. It’s the old principle of KISS: Keep It Simple Stupid. Just do the simplest and easiest technique that works and that would be just running into it with a spacecraft.