There is a small but importantly not insignificant chance that Mars once hosted microbial life, or still does today. For that reason, there are certain areas of the Red Planet that may be off limits to future explorers, robotic or human. These are the Special Regions.
Once thought to be cold and lifeless, Mars now looks like it
could have been habitable. If we want to find out in the future, though, we'll
need to make sure we don't contaminate it with Earth microbes. Thankfully, most
of Mars is deadly to Earth life, but there could be some regions where microbes
hitching a ride on a spacecraft could lead to a false detection of Mars life in
the future.
Thus, scientists drew up the idea of Special Regions. As
defined by the Committee on Space Research (COSPAR) in their 2008 Planetary
Protection Policy, there are regions “within which terrestrial organisms are
likely to propagate or a region that is interpreted to have a high potential
for the existence of extant martian life forms.”
In 2016, this definition was updated slightly to be more
specific. A Special Region now is one that has a water activity rating of 0.5
to 1. Water activity is a measure of how suitable it is for life, dependent on
how easily life could use it for food.
The other main feature of a Special Region is that it has a
temperature warm enough to support terrestrial organisms. This is defined as
being -25°C (-13°F) and higher. There has also been a recommendation to include
methane in the definition, which may support biological life, but that has not
yet been included.
Here’s the kicker, though. We haven’t found a single Special
Region on Mars yet. Zip. Nada.
“There are no Special Regions identified on Mars today,”
John Rummel from the East Carolina University, the lead author on the paper
that redefined Special Regions, told. “We’ve defined them, but we
haven’t found them.”
So what’s the issue? Well, while we haven’t found any such
regions yet, we may well do in the future. And if we do, that could pose some
problems.
We think Mars once had a vast amount of liquid water on its
surface, possibly a large ocean in its northern hemisphere. We also think it
once had a thicker atmosphere, with temperatures and an atmosphere more
conducive to life.
At some point in the last few billion years, Mars lost its
magnetic field and thus its atmosphere for reasons unknown, boiling away the
water on its surface. But underground and even on the surface, there are large
reservoirs of water ice that could contain remnants of that habitable past.
Trickles of water also suggest Mars is not quite dead just yet.
“My guess is that there are places on Mars that could very
well be contaminated by Earth organisms,” said Rummel. “But so far they are
very hard to get to.”
If such regions do exist, then issues will concern how we
clean our spacecraft before we send them there, to eradicate Earth microbes. We
can sterilize spacecraft pretty well, but there’s always a chance some microbes
might sneak along for the ride.
"There are some places where our data are not
sufficient to show they are non-Special. They may exceed the Special conditions
during some parts of the year," David Beaty, Chief Scientist for the Mars
Exploration Directorate at NASA's Jet Propulsion Laboratory in Pasadena, told
IFLScience.
In 2006, a map of the potential Special Regions on Mars was
drawn up. This basically included regions known to have water ice within 5
meters (16 feet) of the surface. This is deemed important because if a lander
crashed on Mars, it would be expected to reach up to 5 meters in depth. As more
ice was found near the equator, the non-special zone began to shrink
However, in that re-evaluation in 2016, it was decided that
you couldn’t really predict where Special Regions would be. Instead, it was
better to look at each region on a case by case basis. So if you want to go
somewhere that looks good for past or present life, then sure, go for it. But
it’ll need to be properly studied first.
“If we found a Special Region on Mars, certainly you’d want
to have kind of a hands-off zone until we fully understood it,” said Rummel.
Spacecraft could still visit these regions, but they’d need
to go through some pretty stringent sterilization procedures first. Under the
COSPAR Planetary Protection Policy, there are five relatively broad categories
of sterilization that spacecraft must adhere to.
At the lower end of this scale is Category 1, for bodies
that that are not of interest in the search for life. These require minimal
sterilization. At the upper end, we’ve got Category IV. This concerns landers
hoping to land in biologically interesting locations on Mars, Europa, and other
important places in the search for life. These spacecraft must be sterilized to
Viking levels.
The Viking 2 spacecraft landed in what was thought to be a
biologically interesting region of Mars, Utopia Planatia, to search for life in
1976. On arrival, the region turned out to be mostly cold and dead (although
water ice was later discovered under the surface). A direct search for life
conducted by the lander – our only direct search for life on Mars to date – was
inconclusive.
Viking 2 went through a very stringent sterilization
process. It was baked in what Rummel describes as an “aluminum casserole dish”
known as a bioshield for 54 hours at a temperature of 101.7°C (215.1°F). If
spacecraft want to go to a Category IV region, they will need to be sterilized
to this level.
A Category V mission, meanwhile, would concern returning a
sample from a biologically interesting world like Mars or Europa. In this case,
not only must the lander be sterilized to Viking levels, but the sample return
capsule must also be isolated from the spacecraft so that it cannot have been
contaminated in any way.
So far, we haven’t really had any issues with Special
Regions. No areas of Mars tick all the boxes, and no one has got very far in
planning a mission to anywhere remotely “special”. A recent study suggested
that the surface of Mars may be even deadlier for Earth microbes than we
thought.
Visiting some locations, like the recurring slope lineae
(RSL), where water appears to be trickling down the surface, is difficult not
because of regulations, but because it’s not easy to design a rover to go up a
slope. NASA’s Curiosity rover is only now making progress up the gentle incline
of Mount Sharp in Gale Crater, but the RSL slopes are much steeper.
Things could all change in the future if some private
companies are true to their word. Most notably, SpaceX CEO Elon Musk wants to
start sending his own robotic and manned missions in the next decade. This has
prompted some concerns that he would not adhere to the Special Region's
guidelines.
Thanks to the Outer Space Treaty of 1967, though, that
hopefully won’t be a problem. Any entity, public or private, needs permission
from their government before they launch. If Musk wants to land in a Special
Region, he’ll need approval to do so.
The fact remains, though, that we simply haven’t found a
Special Region yet. Our understanding of Mars is ever-changing, and there could
well have been life there billions of years ago. Perhaps, too, Earth microbes
could survive in certain places.
If these places exist, we will have to be extremely careful.
We’re doing a decent job of studying the surface from orbit, and so far most of
Mars looks to be fair game. But somewhere, there might just be a little pocket
of habitability we’ll need to cordon off, and decide our next move.