Since then, NASA has worked feverishly to find out as much as they can. Now they think they know what’s going on.
Mars has an atmosphere. Not much of one, but it’s there. And that air has a small amount of humidity. Martian soil is riddled with perchlorates, which pull water out of the air and hang on to it. Ever dealt with clumped-up salt on a humid day? It’s the same principle. So the air gets a little drier, and the soil gets a little wetter. Thing is, when you mix perchlorates and water, you get briny water. And just like adding anti-freeze to a radiator, perchlorates drive the freezing point of water down. In fact, the freezing point drops so low that the water can remain liquid in the frigid temperatures of Mars.
Water’s heavy, so it seeps into the ground. Over time, it builds up as a small aquifer. Eventually pressure or geological activity causes it to erupt and flow along the surface. This leaves the streaks behind that our hero Luju Ojha discovered. Then what happens to the water?
Believe it or not, despite being well below zero degrees Celsius, it actually boils. When you lower air pressure, you lower the boiling point of water. Once the brine is exposed to Mars’s extremely thin atmosphere (about 1/200th the pressure of Earth at sea level), it boils away, leaving only a salty residue and streaked soil behind. Now the water is back in the atmosphere, and the cycle begins anew.
This is a huge discovery. Most scientists consider liquid water to be a requirement for life. Not all agree, but one thing’s for certain: All life on Earth requires it. Furthermore, everywhere on Earth where there’s liquid water, there’s life. No exceptions. If there’s life on Mars, it’ll be in that briny water, and evidence of it will be in those streaks.
Mars is slightly more likely to have native life than any other alien planet, because it’s physically close to Earth. The two planets frequently exchange material due to astronomical events (which is a fancy way of saying “rocks hitting each other really hard”). Every now and then, Earth or Mars has a massive asteroid impact, one so massive it kicks material completely out of the victim planet’s gravity well and into solar orbit. The rocks and debris wander around the solar system for a while, and some of it falls onto the other planet. We have plenty of meteorites on Earth that were originally from Mars. It’s reasonable to assume Mars can say the same about Earth.
It’s possible (unlikely, but possible) that Earth life hitched a ride on one of those transfers. A particularly hearty bacteria or maybe just a few strands of robust RNA. And maybe, just maybe, it survived re-entry and “infected” Mars. These are some pretty low odds. But however unlikely that scenario is, it’s more likely than life evolving on its own. So if any planet in our solar system is going to have life (other than Earth), it’s probably Mars.
And now we know Mars has liquid water, a requirement for Earth life and for anything that evolved from Earth life. There may be microscopic organisms on Mars that have lived there for millions, maybe billions of years. They could be descendants of Earth’s first little one-celled astronauts that made the harrowing journey to the Red Planet. An alien invasion that happened a long time ago in a galaxy… well… in this galaxy right here.
So what do we do about it? Well, that’s where the arguing begins. We’re going to have two camps of scientists at each others’ throats on the issue. There’s a briny water patch just 50km from the Curiosity lander. That’s within range; she could go there and take a look. So why not do it?
Planetary protection proponents believe we run a significant risk of infecting Mars with modern Earth life. And they believe that’s something we have to be very mindful of. An invasive biological contaminant could displace naturally-evolved life and ruin Mars’s ecosphere (if it has one). To guard against that, NASA does their best to sterilize landers so no Earth life can stow away and cause problems. They did this with Curiosity, but not sufficiently to the liking of planetary protection people. They say Curiosity is too much of a danger, and it could have Earth bacteria aboard. They’re actively blocking any attempt to send Curiosity to the briny patch.
And here we reach the “highly opinionated” portion of this article, where I offer my take:
Are you people out of your minds?
We have a chance to find out if there’s life on Mars with a probe we already have on the planet, and you’re blocking it for fear that Earth life will kill it? Earth and Mars have been exchanging material for literally billions of years. If Earth life is going to infect Mars, it’s happened repeatedly.
At this point, you might be tempted to say, “We may have displaced native life in the landed areas, but not in other areas.” Well, either Earth life is a death sentence to Mars, or it isn’t. If it is, the damage was done long ago. If it isn’t, then it’s safe to inspect the nearby briny patch — the worst we can do is ruin that patch.
We can’t be timid in our exploration of Mars. If you think probes have a lot of bacteria, just wait until we send humans. Or will you block manned missions, too? Should it be our fate to hide on Earth until the end of time, terrified of disturbing extraterrestrial life that might not even exist?
The probe is named “Curiosity” for a reason. Send her to the briny patch. Let’s see what she finds out.