In the frenzy to find life elsewhere in the solar system, Mars or the outer gas giant planets’ active moons are usually the odds-on favorites.
But the dwarf planet Ceres, the largest and most massive body in the Main Asteroid Belt, may have evolved some form of thermophilic subsurface bacteria, researchers now say.
At almost 1000 kms in diameter, icy Ceres is thought to be still warm enough inside to provide clement conditions for at least some sort of bacterial life.
Models suggest that the dwarf planet coalesced within 5 million years of our solar system’s first formative salvos. And the Hubble Space Telescope (HST) has determined that Ceres is likely to be differentiated. That is, with the help of radioactive nuclides, water ice melted into an icy mantle while rocky silicates sank to form its putative inner core.
But from a geophysical point of view, researchers stress that Ceres is not an asteroid but, in fact, an intact, small terrestrial-like icy planet. However, like so many objects in the Main Asteroid Belt, Jupiter’s gravity put a squelch on Ceres’ ability to form a full-sized terrestrial planet.
Even so, its shape appears to be “inflated” relative to what we’d expect from a homogeneous body of equal density throughout says Lucy McFadden, a planetary scientist at NASA’s Goddard Space Flight Center. She says it’s probable that a mantle of water ice beneath the dwarf planet’s surface is causing Ceres to expand.
“Ceres likely had an environment that could have supported life; including internal heat and a salty liquid water ocean,” said planetary physicist Thomas McCord, Director of the Bear Fight Institute in Winthrop, Washington. “Mixing of liquid water and silicates created a whole lot of chemistry that made other minerals; [such as], clay-like silicates, and perhaps some salts and carbonates.”
However, when NASA’s Dawn spacecraft reaches Ceres in April 2015, planetary scientists will learn more during almost a year of planned orbital observations.
Ceres probably has a greater percentage of water than Mars, says UCLA space physicist Christopher Russell, the Dawn mission’s Principal Investigator. Russell notes that Ceres may even have a weak atmosphere due to recent hydrous activity from surface geysers, plumes, and/or fountains.
Will we see craters at all or do they last only a short while on this surface? Russell asks. Is there ever rain on Ceres? Snow? Winds?
Ceres has seen its own share of weather, says McFadden, but whether it happens slowly over billions of years, or is actively changing today remains a mystery.
For decades, planetary scientists have been handicapped by a paucity of data about the dwarf planet, which was first discovered in the Main Asteroid Belt over 200 years ago.
It's hard to get really high resolution images or spectra from the ground for such a small, bright object, says Britney Schmidt, a planetary scientist at Georgia Tech. With ground-based imaging of Ceres, she says it’s currently impossible to resolve anything more than 50-km patches.
Schmidt says spectrometry of Ceres’ surface during Dawn’s orbital mapping of the object will allow researchers to see much greater detail, enabling them to search particular areas of the surface for different compositions and properties.
Dawn’s gravity science will tell us how Ceres' interior is put together, Schmidt adds, while finally ending debate over whether it’s a ball of porous rock, or more likely an icy body that's undergone global planetary processes.
Ceres “stretches” our concept of what makes places habitable, says Schmidt. And more importantly, she says, tells us more about water in the forming inner solar system.
“Lets’ say Dawn makes some exciting discovery,” said Russell, “it would take a decade before we got approval for a robotic follow-on mission and another decade to get it implemented.”
Then if a robotic surface probe reported water on the surface and positive signs of life, Russell says astronauts would likely be dispatched for a surface landing sometime after mid-century, likely as late as 2060.
McCord says life may even exist today in a residual, liquid ocean near the top of the Ceres’ silicate core. Or, as Russell notes, in the form of thermophilic bacteria around a hydrothermal vents beneath Ceres’ ubiquitous layers of water ice.
“Although Ceres doesn’t have molten magma, there is heat inside,” said Russell. “So, I wouldn’t rule out life.”
