Science news article: "Bacteria could survive underground on Mars for hundreds of millions of years, new study finds". The article is located at https://www.livescience.com/mars-microorganisms . It says in part the following.
'New research suggests that signs of ancient Martian life could be out
there – or rather, hidden just beneath the Martian surface, safe from
harmful radiation.
... As Elton John once sang, "Mars ain't the kind of place to raise your
kids; in fact, it's cold as hell." But new research suggests that
Martian chill could allow bacteria to survive for up to 280 million
years below the planet's surface.
The
finding raises hopes that traces of ancient life — or even viable
organisms in suspended animation — could be found on the Red Planet
someday.
In the study, scientists found that an Earth bacterium,
Deinococcus radiodurans, is
so resistant to radiation that it can handle the equivalent of 280
million years of the radiation present 33 feet (10 meters) below the
Martian surface. The plucky little microorganism, which has been found
thriving in nuclear reactors on Earth, could even last 1.5 million years
on the Martian surface, which is constantly bombarded with cosmic and
solar radiation.
The key to this survival is Mars' dry, cold environment. When desiccated
and frozen to minus 110.2 degrees Fahrenheit (minus 79 degrees Celsius)
— the temperature of dry ice and the higher-latitude regions of Mars — D. radiodurans "become phenomenally, astronomically radiation-resistant," said study senior author Michael Daly, a geneticist and radiation biology expert at Uniformed Services University in Maryland.'
See also the article called "Caves of Mars Project" located at https://en.wikipedia.org/wiki/Caves_of_Mars_Project and see the article called "Martian cave entrances may offer a life-friendly radiation shield" located at https://www.newscientist.com/article/2288037-martian-cave-entrances-may-offer-a-life-friendly-radiation-shield/ . The latter article says in part the following.
"However, images of the planet from orbit have shown what appear to be entrances to caves, and the insides of these caverns could be protected from those harmful rays.
... The consequences of this are twofold: caves may be safe locations for
human explorers to hide from the extreme conditions at the Martian
surface, and they may also be some of the best places to search for
signs of life on the Red Planet.
No lander or rover has ever visited a cave on Mars, but doing so would
be the best way to figure out whether they really are habitable, says
Viúdez-Moreiras."
These reports are great news folks, and they give great support to my idea which I posted a year ago on this topic thread!