Venus is in some ways the forbidden planet of our solar system. In size and mass, it is a near twin of Earth. Yet, it resembles the popular image of hell; its surface bakes at some 800 degrees Fahrenheit beneath a carbon dioxide atmosphere that’s 90 times denser than Earth’s with an endless rain of sulfuric acid.
Space probes have survived there just long enough to send back images of Venus rocks scattered across a volcanic landscape.
A Planet With a Past
As Space.com reports, Venus may not always have been so hellish. Planetary scientists believe that conditions were much less extreme on early Venus. The dense greenhouse atmosphere with its blistering heat had not yet formed. While Venus, being closer to the sun, was always hotter than Earth, the sun itself was fainter in its early days.
Thus, Venus may once have had liquid water — perhaps rivers and seas, possibly even life on its surface — before volcanic eruptions built up enough CO2 to trigger a runaway greenhouse effect and boil off any oceans it had. Indeed, according to National Geographic, recent tantalizing hints of the organic gas phosphine, high above the clouds, might even indicate that some form of life still hangs on there — all the more reason why scientists would love to know more about Venus’s distant past.
A Tough Place to Get To
A lot of our questions could be answered if only we could obtain some Venus rocks for closer geological and chemical study. As Space.com notes, liquid water has distinctive chemical effects on rocks exposed to it, and these effects remain even after the water is long gone.
The bad news is that bringing rocks back from Venus is so difficult that it’s impractical with current space technology. A prospecting mission would not only have to recover Venus rocks from its hellish surface, but also launch itself back into space against Venus’s gravity, which is nearly as strong as Earth’s.
The good news is that we might be able to find and examine Venus rocks without having to haul them back from Venus. Over the four and a half billion years since the solar system formed, planets have been hit multiple times by asteroids and comets. The most famous of these is the asteroid that hit Earth and wiped out the dinosaurs, but many others are known.
These impacts blasted giant craters on the planets they hit, and some of the material was blasted out so fast that it escaped into space, going into orbit around the sun. In turn, some bits of this material eventually fell as meteorites on other planets. We know this because some of this debris landed on Earth, including a piece of Mars rock that ended up in Africa.
Looking for Venus on the Moon
If bits of Mars could fall onto Earth, so could bits of Venus. But searching for interplanetary debris such as stray Venus rocks on Earth has its challenges. While we got lucky with the Mars meteorite, Earth is not a good museum for preserving space fragments. Earth’s active geology grinds down rocks with wind and water erosion or buries them under deep layers of sediment.
A much better place to look might be Earth’s nearest neighbor in space, the moon. Rocks on the moon have a much better prospect of surviving intact for millions or even billions of years than similar rocks on Earth.
The heavily cratered lunar surface is a testament to a world that, since its formation, has not only been shaped primarily by space impacts but has also endured almost none of the same weathering forces that have “repaved” so much of Earth’s surface. Thus, Venus rocks on the moon are much more likely to have survived intact.
There is even a slight possibility that rocks collected by the Apollo astronauts already contain bits of Venus. But, in any case, future space missions will bring back additional lunar rocks for examination as we look to the moon to understand the second planet from the sun.