Artist's impression of a bolide impact on a young Venus. Credit: SwRI
Venus and Earth have several things in common. Both are terrestrial planets composed of silicate minerals and metals that are differentiated between a rocky mantle and crust and a metal core. Like Earth, Venus orbits within our Sun’s circumsolar habitable zone (HZ), though Venus skirts the inner edge of it. And according to a growing body of evidence, Venus has active volcanoes on its surface that contribute to atmospheric phenomena (like lightning). However, that’s where the similarities end, and some rather stark differences set in.
In addition to Venus’ hellish atmosphere, which is about 100 times as dense as Earth’s and hot enough to melt lead, Venus has a very “youthful” surface. Compared to other bodies in the Solar System (like Mercury, the Moon, and Mars), Venus’ surface retains little evidence of the many bolides impacts it experienced over billions of years. According to new research from the Southwest Research Institute (SwRI) and Yale University, this may result from bolide impacts that provided a high-energy, rejuvenating boost to the planet in its early years.
It’s no secret that Earth was bombarded with plenty of meteors for billions of years during the solar system’s early formation. Estimates vary on how much material impacted the planet, but it had a considerable effect on the planet’s atmosphere and the evolution of life. Now, a new study from a team led by researchers at the Southwest Research Institute puts the number at almost ten times the number of previously estimated impacts. That much of a difference could dramatically change how geologists and planetary scientists view the early Earth.
We can’t just go into space with a big butterfly net or catcher’s mitt, so how in the world could we capture an asteroid?
Ah asteroids, those dinosaur-killing, Scrooge-McDuck-moneybins from heaven.
They’re great and all, but you know what would be better? All the asteroids gathered up and put in a nice safe orbit where we harvest out all their precious sweet, juicy platinum cores.
Instead of nervously scanning the heavens, wishing we had more iridium at our disposal, we could seek out all the asteroids in the Solar System and push them somewhere we can get at them, whenever we want after we dump them into the orbital equivalent of a lazy susan.
Okay fine, instead of pushing all the asteroids around, maybe we should start with one. Get that right and we can extend our plans to the rest of the delicious space rocks we crave.
I know this sounds like just another pie in the sky “Fraser-Cain-double-plus-crazy” plan, but I’m not the only one to propose this idea. In fact, NASA has expressed plans to reach out and capture an asteroid and maybe put it into orbit around Earth.
There are many benefits to this plan. We’ll learn just how hard it is to move asteroids around, should we find one on a dangerous trajectory. We’ll learn how to land on an asteroid, and extract its precious resources. And of course, there’s the science. So much to learn from a pet asteroid. Also, if anyone ticks us off we can lop off clumps and hurl it at them. So a dinosaur killing space rock, returned safely to Earth? That sounds a little dangerous. Possibly a species-wide Darwin awards moment.
An artist’s conception of a space exploration vehicle approaching an asteroid. Credit: NASA
How exactly does one capture an asteroid, and how could we move it back to Earth without killing us all, and more importantly will the Aliens have Darwin awards when we accidentally wipe ourselves out? This sounds like a job for BRUCE WILLIS.
As you may suspect, scientists have come up with a vast collection of clever ideas to move asteroids around. They all come down to the same challenge. You somehow need to impart a thrust to an asteroid. NASA has also informed me that involving Bruce Willis is optional, despite my insistence and extensive letter writing campaign.
One basic idea would be to fly down to the asteroid and install some kind of thruster on it. Perhaps an efficient ion engine, or a rail gun that throws off chunks of rock into space, imparting a thrust to the asteroid. The problem is that asteroids are often spinning, so you’d need to stop that rotation before you could fire up the thrusters.
Artist concept of an impactor heading towards an asteroid. Credit: ESA
Another idea would be to set off nuclear explosions nearby and just push it in the right direction with raw explosive power. By setting off the nuke close enough to the asteroid’s surface, you expel vaporized rock, which acts like a thruster. Also known as the “Ben Affleck Special”.
This one’s going to sound crazy, but scientists are serious. Airbags. You could bump a large inflated bag against the asteroid again and again to slowly nudge it in the direction you want. The rotation doesn’t really matter because the time you contact the asteroid is so brief.
Don’t like that? How about a gravity tractor? Now I’ve got your attention! You could fly a spacecraft really close to the asteroid, which would then attract it slowly, pulling it in the direction you like. As long as the spacecraft keeps thrusting away from the asteroid, you’ll keep pulling it along like a kite on a string.
These are just some of the big ideas. Scientists have proposed some sort of one sided space graffiti, painting them silver, possibly attaching solar sails, or even vaporizing rock with lasers to provide thrust.
Asteroid mining concept. Credit: NASA/Denise Watt
There’s another idea which deserves mention, and I’m going to warn you right now, it’s pretty terrifying. It’s called aerobraking. Instead of using energy to slow the asteroid and put it into the perfect orbit, we use the Earth’s atmosphere to help asteroids shed a tremendous amount of velocity.
By allowing an asteroid to pass briefly – briefly! – through the atmosphere of the Earth, you could decelerate it significantly. Make a few of these passes and you should be able to get it into a nice safe orbit around Earth. Of course, get it wrong and you crash an asteroid into Earth. So, there’s that. It would absolutely make a mess of our lawn, and we’d be the laughing stock of the local group.
Asteroids are precious resources, just waiting for us to reach out and harvest their minerals. Fortunately, we’ve got a range of strategies we can use to move them around. One of them has got to work… right?
Which idea for moving an asteroid do you like the best? Which one really freaks you out?
Earth's Hadean Eon is a bit of a mystery to us, because geologic evidence from that time is scarce. Researchers at the Australian National University have used tiny zircon grains to get a better picture of early Earth. Credit: NASA
During the Hadean Eon, some 4.5 billion years ago, the world was a much different place than it is today. As the name Hades would suggest (Greek for “underworld”), it was a hellish period for Earth, marked by intense volcanism and intense meteoric impacts. It was also during this time that outgassing and volcanic activity produced the primordial atmosphere composed of carbon dioxide, hydrogen and water vapor.
Little of this primordial atmosphere remains, and geothermal evidence suggests that the Earth’s atmosphere may have been completely obliterated at least twice since its formation more than 4 billion years ago. Until recently, scientists were uncertain as to what could have caused this loss.
But a new study from MIT, Hebrew Univeristy, and Caltech indicates that the intense bombardment of meteorites in this period may have been responsible.
This meteoric bombardment would have taken place at around the same time that the Moon was formed. The intense bombardment of space rocks would have kicked up clouds of gas with enough force to permanent eject the atmosphere into space. Such impacts may have also blasted other planets, and even peeled away the atmospheres of Venus and Mars.
In fact, the researchers found that small planetesimals may be much more effective than large impactors – such as Theia, whose collision with Earth is believed to have formed the Moon – in driving atmospheric loss. Based on their calculations, it would take a giant impact to disperse most of the atmosphere; but taken together, many small impacts would have the same effect.
Artist’s concept of a collision between proto-Earth and Theia, believed to happened 4.5 billion years ago. Credit: NASA
Hilke Schlichting, an assistant professor in MIT’s Department of Earth, Atmospheric and Planetary Sciences, says understanding the drivers of Earth’s ancient atmosphere may help scientists to identify the early planetary conditions that encouraged life to form.
“[This finding] sets a very different initial condition for what the early Earth’s atmosphere was most likely like,” Schlichting says. “It gives us a new starting point for trying to understand what was the composition of the atmosphere, and what were the conditions for developing life.”
What’s more, the group examined how much atmosphere was retained and lost following impacts with giant, Mars-sized and larger bodies and with smaller impactors measuring 25 kilometers or less.
What they found was that a collision with an impactor as massive as Mars would have the necessary effect of generating a massive a shockwave through the Earth’s interior and potentially ejecting a significant fraction of the planet’s atmosphere.
However, the researchers determined that such an impact was not likely to have occurred, since it would have turned Earth’s interior into a homogenous slurry. Given the appearance of diverse elements observed within the Earth’s interior, such an event does not appear to have happened in the past.
A series of smaller impactors, by contrast, would generate an explosion of sorts, releasing a plume of debris and gas. The largest of these impactors would be forceful enough to eject all gas from the atmosphere immediately above the impact zone. Only a fraction of this atmosphere would be lost following smaller impacts, but the team estimates that tens of thousands of small impactors could have pulled it off.
Artist’s concept of the early Earth, showing a surface pummeled by large impacts. Credit: Simone Marchi
Such a scenario did likely occur 4.5 billion years ago during the Hadean Eon. This period was one of galactic chaos, as hundreds of thousands of space rocks whirled around the solar system and many are believed to have collided with Earth.
“For sure, we did have all these smaller impactors back then,” Schlichting says. “One small impact cannot get rid of most of the atmosphere, but collectively, they’re much more efficient than giant impacts, and could easily eject all the Earth’s atmosphere.”
However, Schlichting and her team realized that the sum effect of small impacts may be too efficient at driving atmospheric loss. Other scientists have measured the atmospheric composition of Earth compared with Venus and Mars; and compared to Venus, Earth’s noble gases have been depleted 100-fold. If these planets had been exposed to the same blitz of small impactors in their early history, then Venus would have no atmosphere today.
She and her colleagues went back over the small-impactor scenario to try and account for this difference in planetary atmospheres. Based on further calculations, the team identified an interesting effect: Once half a planet’s atmosphere has been lost, it becomes much easier for small impactors to eject the rest of the gas.
The researchers calculated that Venus’ atmosphere would only have to start out slightly more massive than Earth’s in order for small impactors to erode the first half of the Earth’s atmosphere, while keeping Venus’ intact. From that point, Schlichting describes the phenomenon as a “runaway process — once you manage to get rid of the first half, the second half is even easier.”
This gave rise to another important question: What eventually replaced Earth’s atmosphere? Upon further calculations, Schlichting and her team found the same impactors that ejected gas also may have introduced new gases, or volatiles.
“When an impact happens, it melts the planetesimal, and its volatiles can go into the atmosphere,” Schlichting says. “They not only can deplete, but replenish part of the atmosphere.”
The “impact farm:, an area on Venus marked by impact craters and volcanic activity. Credit: NASA/JPL
The group calculated the amount of volatiles that may be released by a rock of a given composition and mass, and found that a significant portion of the atmosphere may have been replenished by the impact of tens of thousands of space rocks.
“Our numbers are realistic, given what we know about the volatile content of the different rocks we have,” Schlichting notes.
Jay Melosh, a professor of earth, atmospheric, and planetary sciences at Purdue University, says Schlichting’s conclusion is a surprising one, as most scientists have assumed the Earth’s atmosphere was obliterated by a single, giant impact. Other theories, he says, invoke a strong flux of ultraviolet radiation from the sun, as well as an “unusually active solar wind.”
“How the Earth lost its primordial atmosphere has been a longstanding problem, and this paper goes a long way toward solving this enigma,” says Melosh, who did not contribute to the research. “Life got started on Earth about this time, and so answering the question about how the atmosphere was lost tells us about what might have kicked off the origin of life.”
Going forward, Schlichting hopes to examine more closely the conditions underlying Earth’s early formation, including the interplay between the release of volatiles from small impactors and from Earth’s ancient magma ocean.
“We want to connect these geophysical processes to determine what was the most likely composition of the atmosphere at time zero, when the Earth just formed, and hopefully identify conditions for the evolution of life,” Schlichting says.
Schlichting and her colleagues have published their results in the February edition of the journal Icarus.
