Arecibo was most often thought of as a radio telescope, but the observatory, which collapsed this week, was also a radar telescope. As such it was a key part of our planetary defense network.
Planetary defense is in its infancy, but the goal is to ensure that we don’t go the way of the dinosaurs by detecting and ultimately deflecting dangerous objects before they hit the Earth.
Arecibo was not the only facility used to track asteroids, but its loss will put a dent in the program.
Yet, there’s some amazing work being done in planetary defense. NASA is already weighing options for an Arecibo replacement, which will likely be similar to the newer Goldstone facility.
So, let’s start by talking about that.
The Goldstone Deep Space Communications Complex
The Goldstone complex’s primary purpose is not planetary defense…it’s communicating with long distance probes.
However, the site also holds the Goldstone Solar System Radar. This uses a 500-kEW X-band transmitter and low-noise receiver attached to a 70-m antenna. (This is considerably smaller than Arecibo’s dish, obviously).
The radar system has been used to locate sites for Mars landers, but also to image and track asteroids. This makes Goldstone part of our planetary defense network; not only does it track asteroids, but it tells us what they look like and, key, helps us determine what they are made of.
When an asteroid turns into a meteorite, the effect of the impact varies according to it’s size and composition. We are actually hit by a meteorite every thirty seconds. But these objects are about 1mm across. They’re essentially dust. They make the Earth slightly bigger over time, but we don’t really notice them. Because they’re so small, they don’t burn up in the atmosphere.
At the other end of the extreme on size, are the big ones, objects larger than 1km. The Chicxulub impactor, the one which took out the dinosaurs, was somewhere between 11 and 81 kilometres in diameter. Yes, that’s still as close as we can get. It wasn’t a planet killer, because a lot of life did survive, but we tend to think of it as one. If there were dinosaurs on the road to developing intelligence (likely), it was certainly one to them.
An actual planet killer, one which destroyed all life on Earth, would have to be at least 96km wide.
But size, while it matters a lot, is not the only factor here. So, let’s compare rock versus iron (a lot of meteors are made of iron. Space is iron-y.
For a (scary) 1km rock hitting sedimentary rock, the crater size per the down2earth simulator (which you can Google as I would lose ranking for linking because they haven’t secured the link is 548m. If I change it to iron without changing anything else, it goes up to 645m.
In the event of a small impact, this would help us determine who needed to evacuate.
So, Goldstone helps us track the location, speed, and composition of rocks. But ideally, we don’t want rocks to hit us at all. Because, bad things happen.
Most people outside Russia had not heard of Chelyabinsk prior to 15 February, 2013.
That was the date it gained the unfortunate distinction of being the first city to be hit by a meteor in the modern era.
The rock that hit was a superbolide that hit at a shallow angle. Rather than hitting the ground, it produced an air burst at 97,000 feet above the city. That’s good, right?
It’s better than a crater, but the air burst produced a shock wave that injured 1,500 people (mostly people who were looking out the window at the fireball, if you want to know what not to do) and damaged over 7,000 buildings. In the middle of a very cold winter.
This was a very minor strike. The rock was 66 ft in diameter. We didn’t see it coming.
If we had, then we would have been able to warn everyone in Chelyabinsk to stay away from windows…
A larger object could have destroyed the city. Chelyabinsk reminded us that evacuation might not be enough.
So, what can we do?
Asteroid Diversion and the Unexpected Role of Latvia
The ultimate goal of planetary defense is not just to track rocks so you can avoid being under them (which works for small rocks, but not ones which are going to create global effects such as an asteroid winter), but deflect them.
Tracking tells us which rocks we need to worry about, but we have yet to successfully change the orbit of an asteroid.
In fact, we have yet to try.
Next year, NASA will launch the first stage of the AIDA mission. The planned launch date is in July. AIDA will use a very simple method of deflecting an asteroid…shooting an impactor at it. (Other proposed methods include attaching a spacecraft to an asteroid and having it fire its engines and using white paint to change the albedo on one side so the solar wind can do the job for us).
The targeted asteroid is never going to be a danger. In 2024, Hera will be launched to look and see whether we actually did it.
Which is where, of all places, Latvia comes in. See, during the Soviet era, Latvia was a great location to track American spy satellites…and in the post-Soviet era, some Latvians have leveraged that history.
In fact, one of the most precise devices to track satellites is created by a Latvian start-up, Eventech. By hand. Because robots can’t do it yet. They sell these devices to observatories who need to remove satellite “noise” from their observations.
ESA has now hired them to create the precise instrumentation needed to determine whether, and how much, the target asteroid (known as Didymos) is deflected.
If AIDA succeeds then the era of planetary defense truly begins.
It’s just sad that it begins without a key part of its history.