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Earth life may have traveled to Venus aboard sky-skimming asteroid

This image of Venus was created using data that NASA's Mariner 10 spacecraft collected on Feb. 7 and 8, 1974, shortly after the spacecraft's closest approach to Venus on Feb. 5.
This image of Venus was created using data that NASA's Mariner 10 spacecraft collected on Feb. 7 and 8, 1974, shortly after the spacecraft's closest approach to Venus on Feb. 5.
(Image: © NASA/JPL-Caltech)

If there is indeed life on Venus, it may have come from Earth — aboard an asteroid that scooped up microbes high in our skies, a new study suggests.

Last week, researchers announced the detection of the potential biosignature gas phosphine in Venus' atmosphere, at an altitude where temperatures and pressures are similar to those at sea level here on Earth. 

Exotic chemical reactions that have nothing to do with life may be generating the phosphine, the discovery team said. But it's also possible that the gas is being churned out by microbes hovering in Venus' sulfuric-acid clouds.

Related: Venus' clouds join shortlist for potential signs of life in our solar system

Those microbes, if they exist, could be part of Earth life's family tree. Lots of Earth material has made its way to Venus over the eons, after all — chunks of planet that were blasted into space by comet or asteroid impacts and ended up getting caught in the second rock from the sun's gravitational grip. 

Many microbe species are incredibly hardy, so it's not crazy to think that some of them may have survived this arduous interplanetary journey intact, astrobiologists say. (Huge amounts of Mars rock have come our way in similar fashion, leading some researchers to speculate that Earth life may actually trace its lineage to the Red Planet.)

But you may not need a destructive impact to send Earth microbes on their way to Venus. A sky-skimming near miss could do the trick, Harvard University's Amir Siraj and Avi Loeb suggest in the new study. 

Earth-grazing asteroids

Siraj, a Harvard undergraduate student, and Loeb, who heads the university's astronomy department, drew inspiration from a July 2017 meteor that lit up the skies over Western Australia and South Australia. That fireball was caused by a roughly 12-inch-wide (30 centimeters), 132-lb. (60 kilograms) object that zoomed through Earth's upper atmosphere for 90 seconds, then resumed its trek through deep space, a recent study by a different research team concluded. 

Such Earth-grazing asteroids could potentially transfer life from our planet to worlds circling other stars, Siraj and Loeb argued in a paper published this past April. (Loeb thinks quite a bit about how life could jump from world to world, an idea known as panspermia.) 

The July 2017 meteor likely picked up about 10,000 microbial colonies during its time in our sky, Siraj and Loeb determined. They performed other calculations as well, estimating the abundance of Earth grazers in the roughly 12-inch size class and how often such objects get slingshotted out of our solar system.

"The total number of [potentially life-bearing] objects captured by exoplanetary systems over the lifetime of the solar system is 10^7 to 10^9, with the total number of objects with the possibility of living microbes on them at the time of capture estimated to be 10 to 1,000," Siraj and Loeb wrote in the April study, which appeared in the journal Life.

After the phosphine find was announced, the duo ran the Earth-grazing numbers again, but this time with Venus as the destination for the putatively transferred microbes. The results are intriguing. Over the last 3.7 billion years (the span in which the asteroid belt has been in a stable state), at least 600,000 rocks that dipped into Earth's upper atmosphere likely hit Venus after spending less than 100,000 years in deep space — a time frame many hardy microbes should be able to handle.

And the numbers are about the same in the opposite direction, suggesting that life could potentially have hopped to Earth aboard Venus-grazing rocks.

"This potentially viable mechanism for transferring life between the two planets implies that if Venusian life exists, its origin may be fundamentally indistinguishable from that of terrestrial life, and a second genesis may be impossible to prove," Siraj and Loeb wrote in the new study, which they just submitted to The Astrophysical Journal Letters. The paper has not yet been accepted for publication, but you can read a preprint of it for free at arXiv.org.

Related: 7 theories on the origin of life

More research needed

To be clear: Siraj and Loeb are not claiming that life definitely has hopped from Earth to Venus, or vice versa. But they hope their paper spurs greater investigation of this possibility.

Now that scientists have spotted a possible biosignature in Venus' air, "it's about time to start thinking a little bit more carefully about what the channels might actually be for the exchange of life, because these planets are so close and so many rocks can be exchanged," Siraj told Space.com.

And the Earth-grazing channel appears to have some distinct advantages over the impact-ejecta one, he added. For example, microbes picked up by Earth grazers won't be subjected to nearly as much heating and shock as their blasted-out brethren.

Still, much more research is needed before the Earth-Venus picture, or the one concerning panspermia more broadly, can be brought into clearer focus. 

For example, scientists still don't understand exactly how impacting objects break apart in planetary atmospheres, Siraj said. And, while we know that microbes are found high in Earth's atmosphere, the abundance of these sky dwellers is not well known, he added.

Then there's Venus. Scientists think the planet was relatively Earth-like for long stretches in the ancient past, before a runaway greenhouse effect transformed the Venusian surface into a lead-melting hellscape. But the timing and other details of this transition remain elusive, so the planet's true astrobiological potential, both now and in the past, is tough to assess.

We may get some important new data soon, however. California-based company Rocket Lab plans to launch a mission to Venus in 2023, to hunt for signs of life in the benign slice of atmosphere where the phosphine was spotted.

Rocket Lab is working with the phosphine team on possible instrumentation for the 2023 effort, which might be just the beginning of an exciting exploration campaign. "We don't want to do one mission — we want to do many, many missions there," Rocket Lab founder and CEO Peter Beck told Space.com last week.

Mike Wall is the author of "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook. 

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  • rod
    The report of phosphine detection in the atmosphere of Venus, kicked off a large amount of press lately. I did some digging into a number of reports on this important finding used to support astrobiology and the hypothesis of abiogenesis. Jupiter and Saturn are reported to contain phosphine or PH3 in their atmospheres too. Here is a report indicating that phosphine is known at Jupiter and Saturn. 'Phosphine on Jupiter and Saturn from Cassini/CIRS', https://ui.adsabs.harvard.edu/abs/2009Icar..202..543F/abstract, August 2009
    Reply
  • just_some_dude
    Looks like this article touches on this topic: https://www.space.com/phosphine-venus-clouds-chemical-explained.html
    "Phosphine is a chemical compound made up of one atom of phosphorus and three atoms of hydrogen, and scientists have also spotted it on Earth, Jupiter and Saturn. On the gas giants, it's quite prevalent in the atmospheres, both of which are rich in hydrogen. On Earth, where the atmosphere leans more toward oxygen compounds, it's much shorter-lived, and the same ought to be true on Venus. "
    Reply
  • tenchi
    Admin said:
    If there is indeed life on Venus, it may have come from Earth — aboard an asteroid that scooped up microbes high in our skies.

    Earth life may have traveled to Venus aboard sky-skimming asteroid : Read more
    The last time I checked, asteroids entering even the fringes of the atmosphere reach over 2k degrees F. It is hard to imagine any life surviving that.
    Reply
  • just_some_dude
    tenchi said:
    The last time I checked, asteroids entering even the fringes of the atmosphere reach over 2k degrees F. It is hard to imagine any life surviving that.

    The paper linked in the artice has a section titled "MICROBIAL SURVIVAL": https://arxiv.org/pdf/2009.09512.pdf
    Reply
  • tenchi
    tenchi said:
    The last time I checked, asteroids entering even the fringes of the atmosphere reach over 2k degrees F. It is hard to imagine any life surviving that.

    I just checked the reference cited by the authors. It is a paper from 2004 by Napier, W. M. 2004, MNRAS, 348, 46 . Here is an excerpt:

    Boulders more than 20 cm across, ejected from the topmost layers of an impact site, are probably never heated to more than 100◦C in their interiors during the few seconds’ flight time from ground to space, while bacteria seem able to survive the accelerations involved(Mastrapa et al. 2001). Thus bacteria within such boulders will survive ejection into space.

    Ejected into space from impacts, not entering the atmosphere from space.
    Reply
  • Jason Roberts
    Admin said:
    If there is indeed life on Venus, it may have come from Earth — aboard an asteroid that scooped up microbes high in our skies.

    Earth life may have traveled to Venus aboard sky-skimming asteroid : Read more
    What is the probability that an asteroid could have done this?

    It seems highly improbable that an asteroid could skim earth's atmosphere pick up microbes, escape earth gravity, then end up in Venus' atmosphere.
    Reply
  • just_some_dude
    tenchi said:
    Ejected into space from impacts, not entering the atmosphere from space.

    " Furtherwork is needed to investigate the existence and abun-dance of microbial life in the upper atmosphere, partic-ularly at the altitude considered here,∼85 km, at which Earth-grazing object would avoid significant heating. "

    So, their argument hinges on the assertion that object grazing that high up would not get that hot. They argue that a porous object could graze very high up in the atmosphere, pickup any microbes up there in their pores, and in very deep pores >10cm where the temperatures may not get so high the microbes may survive.

    The paper isn't peer reviewed and I'm personally not equipped to say if their reasoning is fully sound. It's a pretty short paper and pretty light on details. They are just pointing out that it's a a possiblity that needs further investigation.
    Reply
  • just_some_dude
    Jason Roberts said:
    What is the probability that an asteroid could have done this?

    It seems highly improbable that an asteroid could skim earth's atmosphere pick up microbes, escape earth gravity, then end up in Venus' atmosphere.


    From the paper: " The asteroid belthas been in steady-state for∼3.7 Gyr, implying that during this period,∼6e5 Earth-grazing asteroids of mass∼60 kg have impacted Venuswithin∼105yr of interacting with the Earth. "

    But they don't try to quantify the chances of those asteroids picking-up microbes.
    Reply
  • Jason Roberts
    just_some_dude said:
    From the paper: " The asteroid belthas been in steady-state for∼3.7 Gyr, implying that during this period,∼6e5 Earth-grazing asteroids of mass∼60 kg have impacted Venuswithin∼105yr of interacting with the Earth. "

    But they don't try to quantify the chances of those asteroids picking-up microbes.
    Yeah, it seems these asteroids need an arbitery trip through gravities to perform these feats, I'm unconvinced there are ANY such occurrences of these SuperRocks, and the paper is just rushed out to oppose the team who discovered the Phosphine .
    Reply