On July 12th, CBS launched Salvation, its newest summer miniseries in the US, dealing with the ramifications of the discovery of an asteroid on course for a collision with Earth in just six months. At the centre of the show are a MIT grad student’s and tech billionaire’s efforts to prevent the impact, while the US Department of Defense has its own planetary defense plans. The second episode aired on July 19th. Interested American viewers can watch previously released episodes on CBS’ Salvation website. Our Asteroid Day Expert Panel (ADXP) kindly offered to provide a commentary. They aren’t television critics and will leave it to others to comment on aspects of the story that don’t directly relate to asteroids and planetary defense. Even with that narrow scope, there was too much material in the first two episodes to tackle in a single blog, so they will post updates throughout the duration of the miniseries.
The Asteroid Day Expert Panel weighs in on Salvation
Rusty Schweickart: We are glad that asteroids are part of the public conversation – that’s why Asteroid Day was created. We are excited about the visibility a major TV series provides the general public to engage in the question of asteroid impacts. This gives us another opportunity to do what we enjoy most: educating and informing people about the science behind asteroids and their impacts on Earth.
Being scientists first and foremost, we would like to clarify some of the series’ science to help the general public better understand how such a deflection mission would work in reality, and recognise what obstacles the main protagonists would actually have to face.
This is intended to increase the story’s value by discussing real-world issues and challenges.
Rusty & Mark: We all (even technical geeks like us) enjoy good storytelling. At the same time – especially where the show is dealing with a serious and potentially real issue – it is important to understand how the events portrayed would be different in real life. This isn’t intended to take away from the enjoyment of the story but rather to increase its value by discussing real-world issues and challenges.
Mark Boslough: In science fiction you do have to to allow for some artistic license or the storytelling just wouldn’t work. Still, I think the details that don’t substantively affect the plot should be as much in line with reality as possible. Those are the details we are focused on.
The undiscovered 7-km asteroid
Rusty: At the centre of the series is a 7-km asteroid that is only discovered about six months prior to its impact on Earth. For an ordinary NEA (near-Earth Asteroid) of that size it is highly unlikely, if not to say a ridiculous, assumption – that such an object would only be discovered with so little warning time. An asteroid of this size, if in an ordinary Earth-crossing orbit, would almost certainly be known decades in advance.
Mark: The show has the object in a comet-like orbit. It was discovered near Jupiter and will impact in 6 months, suggesting an orbit that is very eccentric and stretched out into the distant solar system. That means the object would have a very long orbital period. It would take a very long time – possibly hundreds years or more – to complete each circuit around the sun. When viewed from the Earth, comets tend to look like fuzzy objects because they trail dust and vapour (the “coma”) and asteroids look like points of light. The scientists in the show refer to the threatening object as an asteroid, so it must look like a point of light with no coma in their images. But since it’s in a cometary orbit, astronomers in real life would probably be calling it a comet.
There is less than a 1% chance that an existing 7-km Earth-crossing asteroid has not been discovered.
Planetary scientist Alan W. Harris estimates that there is less than a 1% chance that an existing 7-km Earth-crossing asteroid has not been discovered. This would require that it is in an Earth-like orbit and out of phase (or in some kind of resonance that puts it behind the sun at every perihelion – the point in the orbit of an asteroid at which it is closest to the sun). But that’s not the case here, because this object was discovered near Jupiter.
As for time from Jupiter to the Earth, the minimum time to “fall” from the distance of Jupiter to the Earth in a bound orbit would be around 3/4 of a year. Other trajectories could be much slower, but anything faster would require speeds greater than required to escape from the solar system. However the six months to impact as described in the story is not much shorter than the minimum time from a bound orbit, for example an object can get from 4 AU (arguably “close to Jupiter”) to the Earth in six months. The Salvation object is highly improbable, but not impossible. We have objects discovered and designated initially as asteroids that didn’t show coma until they got a lot closer in. The scenario is not entirely impossible, except that “six months” from “near Jupiter” is a bit too short.
The gravitational tractor (GT)
Rusty: The choice to use a gravitational tractor (see Nature article / Scientific American article / Simulation video) to deflect the asteroid was pretty special since Ed Lu of the B612 Foundation along with Stan Love invented that concept. However, a gravity tractor is NOT the right tool for the job of deflecting a 7-km-diameter asteroid from impacting Earth! A gravitational tractor (GT) will be an essential component of any asteroid deflection campaign but it would be used ONLY to “trim” (i.e. very slightly adjust) a far more robust primary deflection, most likely either a kinetic impact or a (last resort only) nuclear explosion for blast deflection.
I sometimes look at a deflection campaign like doing an appendectomy on an Elephant.
The GT is a very wimpy deflection method for making small but precise adjustments to a deflected asteroid’s new orbit to make sure that it doesn’t return for an impact a few years later due to the gravitational kick it gets as it “just misses” the Earth. A deflection campaign will almost always be a 1-2, where the 1 is a primary, robust (but imprecise) kick from a kinetic impact (to transfer momentum from a spacecraft) or nuclear explosion, and 2 is a subsequent small adjustment to that big kick if the asteroid appears to be headed for an improbable, but possible subsequent impact.
I sometimes look at a deflection campaign like doing an appendectomy on an Elephant. You’ve got to first use a chainsaw to get through the skin, and only when inside do you pull out the scalpel for the fine, precise work!
Clark Chapman: A GT would be able to deal with a body roughly one millionth the mass of the oncoming killer asteroid, and it is simply not credible that this gigantic mismatch of capability would be unknown by the DoD. Given other things that happen in the story, however, I wouldn’t rule out that it will turn out that the DoD actually does know that a gravity tractor can’t work, and that various things apparent in the first episode will turn out to be different.
Repurposing the Io space probe
Rusty: The re-purposed Io spacecraft or probe used as a kinetic impactor (KI) was a really interesting idea to deflect the asteroid. But given the size of the NEO it would still not be robust enough to get the deflection job done even though it would have been a thousand times more effective than a gravity tractor. And by the way, it would not, based on our current understanding, have had any likelihood of fragmenting the asteroid.
Holding the discovery secret
Rusty: The idea that knowledge of an imminent asteroid impact could be held a secret is probably a great dramatic element for an entertainment drama, but it is (thankfully) impossible in reality. Telescopes all over the world are staffed by hundreds of people, including graduate students. They observe dozens if not hundreds of moving objects every night and report them to the Minor Planet Center (MPC) each morning. In most cases they have no clue whether any of them are new or old, big and far away or small and close. But they are immediately put onto a public web page by MPC so that observers all over the world can independently confirm that yes, there is an object there, and provide some more precise coordinates. Many independent people are almost immediately involved and would know about any shocking discovery. A 7-km-diameter asteroid on an immediate collision course would be shocking indeed and known by hundreds of people almost simultaneously. And it would be all on public websites. No way to make it secret, it’s out of the bag from the get-go. NASA and other space agencies fully understand that transparency about hazardous asteroids is the only option for both ethical and practical reasons.
Rusty: In the second episode the show came up with an interesting “mechanism” in order to get their proposed gravity tractor (GT) out to the asteroid faster so that it has more time to accomplish the deflection. This assumes, incorrectly, that a GT if there earlier, can get the deflection job done. Unfortunately that wouldn’t be possible: Even if a GT were there instantly it wouldn’t be able to change the orbit of the asteroid enough to miss the Earth in 186 days. But forgetting that issue, the show picking up the EmDrive is interesting in itself.
The EmDrive is essentially an as yet unproven and controversial concept that would use microwaves to generate an extremely low thrust rocket engine without any exhaust coming out the back end, or any fuel used. It would just produce the microwaves under specific conditions and give you an amazing propulsion system.
For now, the EmDrive is similar to Star Trek‘s Warp Drive.
Mark: Basically, for now, the EmDrive is similar to the Warp Drive of Star Trek lore. Not realistic but necessary to move the plot (we can all agree that no matter what the merit is, it’s not realistic to develop in a month or two). I’m a skeptic of anything that violates Newton’s third law, but it’s a plot device.
For more information on the EmDrive, space.com already wrote an article about the controversial propulsion method in Salvation.
We will keep revisiting Salvation in the coming weeks whenever interesting concepts pop up that our Expert Panel feels need further explanation or insight. Therefore keep coming back here to find out more! In the meantime, you will already find plenty of information about several other topics the series touches on throughout the Asteroid Day website: For more information on various asteroid deflection methods, please visit our page dedicated to these efforts. Rusty Schweickart also wrote an entire blog series about planetary defense that will help to clarify the issue!
Further information on asteroid detection can be found here.
To learn more about asteroids in general, click on this link.