That orbit is not a flawless circle.
But the climate has changed significantly over the course of the planet's 4.6 billion year history and liquid water can not exist on the surface today, so scientists are looking underground.
Editor's note: Friday night marks Mars Opposition.
"Imagine that we're sitting on the Earth - looking at Mars". "We'll still need to drill, still need suction, and given the temperatures on Mars, any exposed liquid water would freeze, so there still needs to be a way to turn ice into water", Padir said. This very almost coincides with its [the earth's] closest approach to Mars as the two objects orbit the Sun. This strong radar reflection was interpreted by the study's authors as liquid water - one of the most important ingredients for life in the Universe. MARSIS measures the echoes of the radio waves, which researchers would then be able to use to decode the structure of the subsurface.
Evidence of water has been seen on Mars many times, but it is usually ancient, fleeting or frozen. Layers of the south polar layered deposits - layers of ice and dust - are seen to a depth of about 1.5 km. "It's a finding that should be closely examined by the rest of the radar community to be sure we can rule out other alternative explanations - something I think the authors have already made an excellent effort at doing", Clifford said.More news: Trump's defense chief says weighs talks with Russian counterpart
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"This subsurface anomaly on Mars has radar properties matching water or water-rich sediments", says Roberto Orosei, principal investigator of the MARSIS experiment and lead author of the paper published in the journal Science.
"That's a fundamental aspect of astrobiology", said Jim Green, chief scientist of NASA, who was not involved in the study. "Now we see things that simply were not possible before", added Cicchetti. This is known as an opposition.
"There's nothing special about this location other than the MARSIS radar on the Mars Express spacecraft is most sensitive to that region", said Duffy.
Scientists are eager to find signs of contemporary water, because such discoveries are key to unlocking the mystery of whether life ever formed on Mars in its ancient past, and whether it might persist today.
It is going to be a treat for the skygazers tonight when a total Lunar eclipse will coincide with Mars' coming closest to the Earth in 15 years.