Bright lights and the possibility of life add mystery to Nasa's Ceres mission

With only days to go before the first probe goes into orbit around this surprisingly interesting dwarf planet, further mysteries – including two strange bright spots in a crater – are coming into focus.

Sign Up

Get the New Statesman's Morning Call email.

In contrast to the exciting news this week that Nasa’s 2016 federal budget allocation includes money for a mission to Jupiter’s moon Europa, Nasa’s Dawn spacecraft is just days away from closing in on Ceres, the dwarf planet almost nobody seems to be talk about. Its name comes from the Roman goddess of corn and harvest, which seems fitting, as it could potentially contain a tantalising buffet of life for astrobiologists to salivate over. And there are other mysteries too, as the first clear images of this unexplored world begin to appear, and there are two bright reflective spots on its surface – and nobody really knows what they are.

Towards the end of the 18th century, astronomers had mathematically postulated the presence of a then-missing body, Ceres, between Mars and Jupiter. In eager anticipation of its discovery, astronomers spun their telescopes to its region. The Sicilian astronomer Giuseppe Piazzi had a new year and new century worth celebrating because, on 1 January 1801, he was the first person to spot it, in the region commonly known as the Asteroid Belt.

Is an asteroid? Is it a planet? No, it’s a dwarf planet. (Yes, like Pluto.) The gravitational disturbance of Jupiter meant that, as the rest of the planets of the Solar System formed out of smaller objects billions of years ago, the asteroids in the Asteroid Belt were never able to clump together – and, while Ceres is rounded under its own gravity and looks like a small planet, it's doesn't qualify because it's unable to gravitationally clear neighbouring objects out of its path. While for much of the 19th century Ceres was seen as a bona fide planet, it had been downgraded to a mere asteroid by the beginning of the 20th  but, as a consolation prize, Ceres was given dwarf planet status in 2006, making it the only dwarf planet in the inner Solar System.

Measuring roughly 900km in diameter (or about the width of Texas), Ceres is by far the largest body in the Asteroid Belt, making up nearly a third of its mass  and its spherical shape and composition make it likely that it formed at the same time as the other planets did during the earliest years of the Solar System. Yet there's a different between it and Earth: water has a density of 1 gram per cubic centimetre, and while Ceres' average density is 2.09g/cm3, Earth’s is 5.5g/cm3. Ceres’ density implies that a higher proportion of it is water than rock, relative to the Earth.

In 2013, the European Space Agency’s Herschel Space Observatory spotted the ejection of water vapour from its surface – either by some kind of geyser or volcano, or because of some process of sublimation. ESA astronomer Michael Küppers wrote of the discovery that it was "the first time water vapour has been unequivocally detected on Ceres or any other object in the asteroid belt, and provides proof that Ceres has an icy surface and an atmosphere". Other scientists, like Jian-Yang Li of the Planetary Science Institute in Arizona, have said that they believe Ceres is "the largest water reservoir in the inner solar system other than the Earth", even if nobody's sure yet what form it's in. There could be a huge liquid ocean beneath the dwarf planet's crust, kept warm by internal convection; or it could be that Ceres is largely frozen ice, like a huge comet.

Regardless, this was great news. Liquid water is the fundamental basis for the biochemistry we know on Earth, and with Ceres also appearing to possess other important chemical elements  like carbon, hydrogen, nitrogen and oxygen  it makes Ceres a decent contender as a possible host of alien life. It adds even more excitement to Nasa's Dawn mission.

Launched in 2007, Dawn was designed to travel to, and study, both Ceres and the second-largest object in the Asteroid Belt, Vesta. It spent 14 months studying the latter between July 2011 and September 2012, mapping its surface and taking extensive measurements, before moving away towards Ceres. It's due to slip into Ceres' orbit on 6 March, but since the beginning of the year, as the dwarf planet has come closer and closer, Dawn has been able to return sharper and sharper images that are already proving intriguing.

Before Dawn, our best image of Ceres came from the Hubble Space Telescope pointing in its direction in 2004, showing us an eerie, misty sphere, with what appeared to be a bright crater or depression of some sort:


Image: Nasa

The early Dawn pictures weren't much better, but when stitched together – as with this series of shots taken on 13 January – the bright feature on the surface is still clearly visible:


Image: Nasa

 

Recently, Nasa's Dawn captured another mysterious bright spot from a distance of nearly 47,000km – making it a total of two bright spots. Planetary scientists have known for a while that regions of higher than average albedo (ie light reflection) exist on Ceres, but have had difficulty interpreting what could be causing them due to the low-resolution transmitted images. In a statesment, Chris Russell, the Dawn mission principle investigator said: "Ceres' bright spot can now be seen to have a companion of lesser brightness, but apparently in the same basin. This may be pointing to a volcano-like origin of the spots, but we will have to wait for better resolution before we can make such geologic interpretations."

As for whether we should get our hopes up about finding microbial life on Ceres now, Dawn mission science liaison Britney Schmidt told the NS:

At this point, there is no real expectation of life on Ceres, though there are those who have played with the idea. It is possible that Ceres had or has an ocean that would be of interest for thinking about prebiotic chemistry. Ceres is an incredibly compelling object to study that impacts our understanding of how planets formed and evolved in the early solar system, and in particular, the history of water on planets and indeed the Earth itself.

Dawn will be able to confirm that Ceres has a huge fraction of ice that makes it like the icy moons of the outer solar system.  All of this is important for humanity because at this point, we don't even know how water was delivered or formed on Earth. Ceres is a big piece of that puzzle!"

Tosin Thompson writes about science and was the New Statesman's 2015 Wellcome Trust Scholar.