Mars was a hot planet with high seas, right?
Now a study says no, Mars was cold and icy, not warm and wet.
According to the new study, scientists looked at opposite climate scenarios of Mars in its early years. The study suggests that if we thought of the planet as cold and icy billions of years ago, it would explain the water drainage and erosion features we see today better.
Researchers have debated for decades on what Mars climate history was and how the many water-carved channels got where they are. Today, it is too cold for any sustained liquid surface water. What we know about the Sun indicates it should have been producing about 25 percent less heat early on then it does now. Carl Sagan even had a study published in Science in 1972 that supported the idea that Mars should have been colder.
Curiosity Rover report—the making of Mount Sharp:
“Previous studies have shown that even when the effects of climate-warming clouds, dust, and carbon dioxide are taken into account, climate models still don’t show early Mars developing any warm and wet periods,” researcher and lead author Robin Wordsworth said, from the Harvard Paulson School of Engineering and Applied Sciences.
But the idea that Mars was once warm, wet, and Earth-like, with a northern sea that had conditions that could have led to life, has remained the more popular scenario. The more plausible thought of it being a frigid, icy planet where water is ice most of the time and life would have been hard to evolve, has been less popular.
NASA Mars Curiosity Rover report:
According to Eurek Alert, to see which early Mars better explains the modern features of the planet, Wordsworth and his colleagues used a 3-dimensional atmospheric circulation model to compare a water cycle on Mars under different scenarios 3 to 4 billion years ago, during what’s called the late Noachian and early Hesperian periods. One scenario looked at Mars as a warm and wet planet with an average global temperature of 10°C (50°F), and the other as a cold and icy world with an average global temperature of minus 48°C (minus 54°F).
“The colder scenario was more straightforward to model,” Wordsworth said, “because Mars only gets 43 percent of the solar energy of Earth, and early Mars was lit by a younger Sun believed to have been 25 percent dimmer than it is today. That makes it very likely early Mars was cold and icy.”
By using the cold model, it explained the water erosion features that we can see now on the surface, which has puzzled and intrigued scientists since first discovered by the Viking orbiters in the 1970s. The study was published in the AGU’s Journal of Geophysical Research—Planets.
“I’m still trying to keep an open mind about this,” said Wordsworth. “There is lots of work to be done. But our results show that the cold/icy scenario matches the surface distribution of erosion features more closely. This strongly suggests that early Mars was generally cold, and water was supplied to the highland regions as snow, not as rain.”
“Proving that a cold climate on early Mars led to the features seen on the planet today is a big question,” said Bethany Ehlmann, a planetary scientist at the California Institute of Technology and NASA’s Jet Propulsion Laboratory in Pasadena, and was not involved in the study.
“We know from rover- and orbiter-based data that there were lakes on ancient Mars,” she said. “Key questions are: How long did they persist? Were they episodic or persistent? And does the feeder valley network demand rain, or is snow and ice melt sufficient?”
There are still and probably always be questions to be answered, but will we ever really know what happened on Mars 3 to 4 billion years ago, and an even a bigger question is, do we really need too?