Space Matter: Venus (Not Mars) is Our Real Sister Planet

With all the talk of going to Mars, you’d be forgiven if you’ve forgotten that the red planet isn’t actually our sister planet. We’ve got rovers crawling the surface of Mars, with more on the way, and our human exploration goals, whether public or private, involve putting humans on the red planet in the next two decades.

But if you take a step back and look at both Mars and Venus, it might appear a little confusing as to why we’re so fixated on visiting Mars, rather than Venus—at least on the surface. After all, Venus is closer to Earth than Mars is. At their closest, Mars is 33.9 million miles away, while Venus is just 24 million miles away from us. That’s not an insignificant difference, especially when you consider the logistics of resupplying permanent settlements.

1.venus.png Venus (credit: NASA)

Venus’ gravity is also similar to ours—8.87 m/s2 versus our own 9.8 m/s2. Mars’, in contrast, is just 3.7 m/s2. Astronauts spend an extraordinary amount of time trying to combat the deleterious effects that weightlessness has on the human body. That wouldn’t be nearly as much of an issue on Venus as it will be on Mars over the medium and long term.

Add to that evidence that Venus was once habitable. Our planets are very similar in density, size, and composition—there’s a good chance that Venus once hosted warm liquid water and it’s possible that simple forms of life could have evolved on the planet.
Our planets are so similar, and likely developed the same way, that scientists have begun to call Venus our “twin.”

Given all this information, why are our sights so narrowly focused on going to Mars, rather than Venus?

Because with a surface temperature of greater than 900 degrees F, Venus is the hottest planet in the solar system. The surface air pressure is about 90 times heavier than Earth’s.

Maat Mons on Venus surface (Image credit: NASA)

The fact is, Venus’ atmosphere is a thick, deadly soup that we still haven’t figured out how to contend with. The planet is hidden by dense clouds; we’ve barely gotten glimpses of the planet’s surface. We’ve sent orbiters to the planet, but every lander that has descended to the surface has been crushed within an hour or two due to the high atmospheric pressure. Additionally, the carbon-dioxide rich atmosphere traps the Sun’s heat in a runaway greenhouse effect, making the temperature on the planet’s surface hot enough to melt lead.

All of this comes down to the fact that it’s simpler to put humans on Mars than on Venus. But that doesn’t mean we should neglect Venus; there are compelling reasons to visit our sister planet that has been somewhat overlooked in recent years, in all our fervor to get to Mars. It’s possible that we could build a permanently inhabited space station in orbit of the planet; after all, 30 miles above Venus’ surface, you’re above most of the cloud layer yet it’s still warm enough for liquid water. And there’s some really interesting stuff to study on Venus.

It’s possible that life actually exists within the clouds of Venus. Scientists want to take a close look at the dark streaks in the planet’s clouds because this could be microbial life. It’s definitely a reach, but one that’s worth exploring. Venus also has electrically charged wind, which may have contributed to stripping the water from the planet’s atmosphere. Not the most welcoming place, perhaps, but you can’t accuse the planet of being scientifically uninteresting.

Could the dark streaks in Venus’ clouds be life? (Image credit: NASA)

All of this being said, it’s understandable why we’re set on going to Mars, rather than Venus. There’s something tactile about actually being able to set foot on a new world, rather than merely exist in orbit of it. And Mars is, quite simply, easier. Yes, issues of supply (given the distance between the two planets) and gravity become a problem for longer term stays, but for our short and medium-term goals, Mars seems more within our grasp than any other planet. “Because we can” might not seem like the best reason to choose Mars over another, more scientifically interesting, world, but we have to start somewhere.

With that in mind, it’s more than time to send another orbiter/lander to study our real sister planet. It’s looking like we might work with the Russians to send Venera-D, an unmanned mission to Venus, though it’s unclear what form it will take. Scientists would love to design a lander that will survive Venus’ harsh surface for more than just an hour, but we don’t quite know how to do that right now. We’re currently planning a tentative launch in 2025 or 2026, but this might be too aggressive, given all the logistics that need to be worked out before the spacecraft can be built. The Russians are in charge of this one—NASA is just along for the ride, and helping out where we can—but it’s a mission that is absolutely worth keeping an eye on.

Top image: NASA

Swapna Krishna is a freelance writer, editor and giant space/sci-fi geek.