Is life in the Solar System unique to planet Earth?


So far, no definitive answer is available, but many astronomers, astrobiologists, and cosmologists believe it is likely that life exists (or has existed) elsewhere in the Universe – and, perhaps, that it is even common.  Using methods and technologies that are advancing rapidly, the scientists’ searches for proof extend from nearby planets and moons to distant star systems.  Over the next couple of weeks, I will survey four possible homes for life within our own Solar System, starting with Mars.

NASA Racks Up Frequent Flier Miles

Well-publicized plans by government agencies and private companies to send humans to the red planet for a look-around are moving forward, with the estimated time of arrival varying from a few years to a few decades hence.  As we await that potentially momentous event, spacecraft have been visiting Mars rather regularly – there are currently three craft in orbit around the planet and two operating rovers on the surface, sending back data and images that are suggestive but inconclusive.

Ripples and small dunes show effect of wind on the surface of Mars. (Image credit: NASA/JPL-Caltech/Univ. of Arizona)

What have we learned?  To date, there is no credible evidence that advanced life has ever existed on Mars.  However, scientists are increasingly convinced that the planet was habitable in its distant past, and some believe that microbial life might continue to survive in suitable pockets (probably below the surface).

Past and Present Prospects for Life

Early in its history, Mars had a fairly dense carbon dioxide atmosphere and a magnetic field, which could have protected against lethal solar and cosmic radiation.  It also had key chemical ingredients thought to be necessary to life.  There is evidence that, 3.8 billion years ago, between 36% and 75% of the Martian surface was covered by water.  The planet was much colder than Earth, but important conditions seem to have been conducive to the possibility of life’s formation.

Purple spots form on dunes where CO2 defrosts at the end of winter on Mars. (Image credit: NASA/JPL/Univ. of Arizona)

Even now, water ice accumulates in the polar regions of Mars, and very briny liquid water could be close to the surface at certain locations.  However, the atmospheric pressure is far too low to sustain liquid water on the surface for longer than a few minutes or hours.  The chances of life currently existing on Mars appear to be lower than the possibility of it having existed there billions of years ago – and perhaps having left traces for robotic or human explorers to find.

Getting to Mars

There are daunting technological, medical, psychological, and logistical challenges to be overcome before human explorers can be sent to Mars and returned safely home.  SpaceX chief Elon Musk has said that his company should be able to begin unmanned missions in 2018, using its Red Dragon spacecraft to pre-position supplies on the planet for later visits by human explorers.  He hopes to send humans in 2024, with arrival in 2025.  NASA supports and hopes to build on the Red Dragon mission, but the agency’s current plans envision sending astronauts no earlier than the 2030s.

“The root of the problem for landing on Mars is this poor excuse for an atmosphere . . .” – Robert Manning, Jet Propulsion Laboratory

SpaceX’s Red Dragon descends into Martian atmosphere in artist’s rendering. (Image credit: SpaceX)

As inspiring as the prospect for human exploration of Mars is for many of us, some thoughtful observers argue that sending astronauts to the planet should be delayed indefinitely – at least until the logistical challenges are addressed more assuredly and the economics of such a mission fall more in line with expected scientific benefits.  For the foreseeable future, they reason, additional robotic missions would yield similar (if not better) results and would be far more cost-effective.

NASA’s Curiosity rover at lower Mount Sharp on Mars. (Image credit: NASA/JPL-Caltech/MSSS)

Here’s a selection of our best SpaceRip videos focusing on Mars.  Enjoy and leave a comment below!