From Jonathan I. Lunine
How tenuous is our planet’s ability to support life? The answer might come from one of our nearest planetary neighbors. Orbiting spacecraft and rovers deployed on Mars over the past twenty years have found strong evidence for conditions billions of years ago that were very different from the dry, cold environment of today. When and why did Mars change? Understanding Mars’ past can give important clues to our own planet’s future.
Today, we are on the threshold of answering these questions. Since 2021, NASA’s Perseverance rover, designed and built by the Jet Propulsion Laboratory (JPL), has been collecting samples to be returned to Earth in a technologically daring mission called Mars Sample Return (MSR) that is currently under development.
And yet, the political storms that have hit Washington, DC, threaten to leave those valuable samples stranded on Mars, by giving NASA far less than it needs to design and build the spacecraft that will return the samples. Unless Congress restores that funding, scientists may never see them. To understand the samples’ inestimable value, we need only look at where Perseverance has landed: a crater named Jezero. At the crater’s western end is a river channel and a huge pile of sediments resembling what geologists call river “deltas,” places on Earth where rivers meet the sea. Today the river channel holds no water, and the delta sits on a dry and barren crater floor. But both are a testament to an ancient time when water flowed on Mars, breaching the crater wall and dumping sediments in a vast crater lake.
Did water flow on Mars long enough for life to have begun? Why did this and other oases dry up, and when? To answer these questions, Perseverance has been collecting samples of the crater floor, the delta and the hills above it. It is guided carefully by a large team of scientists who are the world’s experts in the geology and climate of ancient Mars. The rover itself is a mechanical marvel, drilling into rock and packing the pulverized material into over 30 sample containers the size and shape of laboratory test tubes. Within these tubes are priceless samples of Mars that hold the clues to when and how Mars went from Earth-like habitability to uninhabitable desolation. To tease from these rocks the history of Mars and its climate requires analyzing them in massive, power-hungry and user-intensive instruments here on Earth. These instruments can determine the presence of materials at concentrations unreachable by the much smaller devices carried directly to Mars inside a spacecraft. Terrestrial laboratories are also uniquely capable of precisely measuring the rocks’ ages using a technique called radioisotope dating. Finding the precise ages of moon rocks was among the most important outcomes of the Apollo missions, placing the earliest history of the Earth and moon on an absolute timetable. To be able to construct such a chronology for Martian history as well would be a profound scientific result.
Mars Sample Return is among the most challenging and complex robotic missions ever attempted, requiring the largest lander ever put on Mars, which would carry a rocket to launch the samples off the surface into Martian orbit. Another spacecraft – to be built by the European Space Agency – would pick up the sample capsule in orbit and shuttle it toward Earth. This mission has been named the highest priority in US planetary exploration for the next decade in two major strategic plans by the US National Academy of Sciences. And yet, the return of the samples may never happen.
Perseverance continues to fill its sample tubes, awaiting the day when a ship will come to take these priceless Martian samples home to Mother Earth. Will the US complete its mission or allow an emerging space power such as China to retrieve them? Or will the samples simply be abandoned on Mars? What would be the impact on the nation’s long-standing leadership in deep space exploration if Mars Sample Return were to become the first major space mission we did not complete because of a failure of will? Mars holds secrets about what makes it possible for a planet to support life, locked in the samples that await return to Earth. Just this month Congress reaffirmed MSR as the highest priority of the 2022 Planetary Science Decadal Survey of Planetary Science and tasked NASA with developing a realistic plan and funding profile that will achieve the return of the samples. NASA must provide that plan to Congress as soon as possible so that Congress can move forward with adequate funding. Leaving the samples stranded on Mars would be a national disgrace. –FP
