This true-color Mars globe includes Terra Meridiani, the region where NASA’s Opportunity rover explored from 2004 to 2018.  Two more Mars rovers — one from NASA and the other from China — are scheduled to land this week and then later in the year. (NASA/Greg Shirah)

Mars is receiving visitors these days.  Quite a few of them.

The most prominent visitor is NASA’s Perseverance rover,  which made a difficult but smooth precision landing at 3.55 ET  this afternoon.

The rover now sits in Jezero Crater, in an area that clearly once had lots of water flowing.   The site was selected, in part, because the Perseverance rover’s official mission includes — for the first time since the mid 1970s — an effort to find signs of long ago life.

Perseverance will join the Curiosity rover on Mars, that pioneering machine that has revolutionized our understanding of the planet since it landed in 2012  The Curiosity and Perseverance rovers are similar in design but carry different instruments with different goals.

A key difference:  Curiosity was tasked with determining whether Mars had once been habitable and found that it definitely had been, with flowing rivers, large lakes and necessary-for-life organic compounds.  Perseverance will take another scientific step forward and search for signs that Mars actually was once inhabited.

Perseverance also joins China’s Tianwen-1 (“heavenly questions”) probe,  which went into orbit around Mars last week.  It is the first Chinese spacecraft to arrive at Mars, and later this spring or summer the Chinese space agency will attempt to land a rover as well on the planet’s northern plains..

And then there’s the Hope spacecraft which entered into Mars orbit last week as well.  Launched by the United Arab Emirates, it was placed in a wide orbit so it could study the planet’s weather and climate systems, which means it also can see the full planet in one view.

These spacecraft will join several others on or orbiting Mars, making this by far the busiest time ever for exploration of Mars — a real milestone.

NASA’s Perseverance rover will land in Jezero Crater. This image was produced using instruments on NASA’s Mars Reconnaissance Orbiter, which helps identify potential landing sites for future missions. On ancient Mars, water carved channels and transported sediments to form fans and deltas within lake basins, as is clearly visible at here at Jezaro Crater (NASA/JPL-Caltech/ASU)

That the Perseverance mission has a formal goal of searching for ancient signs of life is a big deal, and involves a lot of history.

The first American spacecraft to land on Mars were Viking 1 and Viking 2, in the mid 1976.  They were an ambitious, and remarkably successful, first try that included two experiments focused on searching for extant life.  This when a time when Mars still lived in the scientific and public imagination as a place where not only life but evolved life might exist.

And while the Viking landers found a parched landscape, one of the life detection experiments did come up with results consistent with NASA’s guidelines for what a detection of life would look like.  Both landers had the same experiment, called Labeled Release, and both came up with the same seemingly positive results for microbial activity in the Martin soil.

But another experiment cast doubt on the Labeled Release results and a bitter scientific feud ensued, confusing the public and greatly frustrating NASA.  The result was that missions to Mars took a back seat for some time and, until Perseverance, no NASA Mars mission has had “life detection” as a formal goal.

After Viking, the agency had concluded that the science and technology needed to arrive at a solid finding of life on Mars was just not in place, and they didn’t want a repeat of Labeled Release.  Only in the last decade or so has that view begun to changed. And while the “life detection” goal of Perseverance reflects a major scientific step forward, it is limited to a search for possible signs of ancient life rather than of currently existing life.

Several new instruments are onboard designed specifically to identify chemical structures in rock that could come from long-ago life — especially the Planetary Instrument for X-ray Lithochemistry ( PIXL) — and they will add a new dimension to Mars exploration.  Perseverance is also bringing with it a tiny helicopter that will, for the first time, test the feasibility of such aerial exploration from a rover.

And Perseverance has the capacity to identify, collect and cache rocks and dirt samples that will, according to NASA plans, be returned to Earth for in-depth study on a future mission.  Many Mars scientists say the question of curre3nt life, or ancient life, on the planet won’t be settled until those samples — and others — can be studied in labs on Earth.


         Early video from the Tianwen-1 probe, which entered Mars orbit last week.  (CNSA)

When it comes to landing on Mars as the beginning of a successful long-term mission, the United States and NASA stand alone.  All of the eight successful missions to the Martian surface have been American.  One spacecraft sent by the former Soviet Union  made a soft landing in the early 1971 but soon after lost communication with Earth.  The same happened with a mission launched by the United Kingdom in 2004 and a European Space Agency lander crashed in 2016.

The effort by the China National Space Administration (CNSA) to join NASA with a successful soft landing and mission brings with it a lot of history as well as promise.  The Tianwen-1 probe is China’s first spacecraft to reach Mars, and it will orbit for several months before sending its lander with a rover inside to the surface.

Utopia Planitia as photographed by the Viking 2 lander in the mid 1970s, with color added later. This is likely to be where Tianwen-1 will attempt to land. (NASA)

The destination for the lander is expected to be Utopia Planitia in the lower northern plains — a flat expanse of volcanic rock in a large basin that is close to where one of the Viking 2 landed 45 years ago.  But much more is known today about the region, and especially the water ice below the surface that is estimated to match the water volume of Lake Superior.

Polygonal, patterned ground is quite common in Utopia Planitia and is commonly believed to be caused by the sublimation of ice from the ground. (Sublimation is the direct change of solid ice to a gas.) This is similar to what happens to dry ice on the Earth. Places on Mars that display polygonal ground may indicate where future colonists can find water ice.

The area is close to the large volcano Elysium Mons, where domes, pitted cones and other land forms have been found that some link to the presence of water or ice.

A topographical map of Mars, with the landing site for Perseverance, the possible “chosen” landing sites for Tianwen-1, and the sites where other American spacecraft have land.  Russian (Mars 2, Mars 6) and British (Beagle 2) spacecraft have landed as well, but not successfully. The northern blue area is where some Mars scientists think a large ocean once existed. (NASA)

Utopia Planitia may also be part of what some scientists have concluded was once a large ocean on northern Mars.  The  discovery of the Martian dichotomy — a roughly 20 mile difference in height between the lower, smooth northern hemisphere and higher, heavily cratered southern hemisphere — was an early indication that the northern hemisphere may once have been underwater.

Long, unbroken features identified as potential ancient shorelines were spotted on Mars as early as the 1970s by the Viking orbiters, further supporting a picture of vast past oceans. And dozens of further clues have piled up: signs of stream channels and river deltas, indications of past rainfall, hints of historical tsunamis from asteroid impacts, atmospheric signatures that point to a past abundant water supply.  But the debate goes on and Tianwen-1 might provide additional information

Artist rendering of the UAE Mars Orbiter “Hope.” (United Arab Emirates)

The United Arab Emirates successfully placed its “Hope” spacecraft in Mars orbit last week.  That brings to seven the number of space satellites currently orbiting Mars — two from the United States, two from the European Union and one from India, China and the UAE.

The UAE orbiter sent back its first images several days ago and the mission’s Twitter account described it as “a defining moment in our history and marks the UAE joining advanced nations involved in space exploration.  We hope this mission will lead to new discoveries about Mars which will benefit humanity.”

Successful space missions are, and always have been, a source of national pride as well as scientific discovery.

Hope will orbit much further out from Mars than most other orbiters, and scientists expect that will allow for some novel research. For instance,  the orbiter is going to trace how energy moves through the atmosphere from the very bottom to the very top.

Another instrument will track the leakage into space of neutral atoms of hydrogen and oxygen – remnants from Mars’ once abundant surface water. This will add to our understanding of precisely how a previously warm and wet planet became so cold and desiccated.

All three missions are reaching Mars as it passes close to Earth — which happens every 26 months due to the differing orbital paths of Earth and Mars.  This proximity decreases cost by cutting travel time to about 7 months.

An artist’s illustration of the landing of Mars rover Perseverance, using a “sky crane” similar to the one that successfully placed the Curiosity rover in Gale Crater in 2012. ( NASA/JPL-Caltech)

The first image from Perseverance after the rover landed on Mars.  It was taken by a logistics camera on the base of the rover: the color and panorama and detailed shots will be coming soon. (NASA/JPL-Caltech)

Other missions to Mars are in the pipeline, though not at the frequency we’re seeing now.  NASA is working with the European Space Agency (ESA) on a campaign to bring Mars rock samples back to Earth, and  ESA and Roscosmos have a second Exo-Mars launch planned for next that will look for signs of past like.

In what would be a first, entrepreneur Elon Musk says he hopes to launch his Starship spacecraft to Mars in 2024.  Planned and now being built by his private company, SpaceX, it would potentially start a new chapter in Mars exploration and eventually colonizing.

Already, space agencies including NASA, ESA, the Chinese Space Agency, the Russian agency Roscosmos and India’s Space Research Organization (ISRO) are all researching how to send humans to Mars and set up colonies, as have SpaceX, Lockheed Martin and Boeing.

Sending humans to Mars won’t happen any time soon. But if it turns out to be technologically possible and safe to an acceptable degree, it would be a natural fulfillment of humanity’s fascination with the one solar system planet that long ago was rather similar to our own.