A Trinity College Dublin geologist has come up with fresh ideas on how space debris and dust manage to form themselves into planets
UNDERSTANDING the origins of our solar system is one of the great questions of science. A “hunch” that is being backed up by hard facts has led Trinity College geologist Dr Ian Sanders to a radical new idea – one that goes against the conventional wisdom.
Our sun, like other stars, was formed from a disk of gas and dust around four and half billion years ago, which is why the planets all lie in the same plane, says Sanders.
The dust and gas in this disk combined to form tiny planets, or “planetesimals”, and ultimately the planets we see today. It is the details of this process that Sanders has studied for the past 15 years.
“The asteroid belt is a region where this process was thwarted – probably because Jupiter was too close. This has led to lots of leftover material,” explains Sanders.
We have access to this material through the meteorites that fall to earth. “Common meteorites formed right in the beginning, providing samples of the material that never made it to planets,” says Sanders.
When meteorites fall to earth they carry with them valuable, ready-made clues called chondrules. Chondrules are grains that formed from molten droplets of rock, like lava, explains Sanders.
“The conventional idea is that they formed when dust was zapped by some unknown source, possibly solar flares. The main reason for this hypothesis is that their chemistry is exactly the same as that of the sun – they are the raw material of the whole solar system,” he says.
He sees flaws in this assumption however. The alternative explanation, that Sanders believes is much more likely, is that chondrules formed when much larger molten bodies collided, “splashing” out tiny droplets of molten rock.
But how did these larger bodies themselves form? And why were they molten if the temperature in the surrounding space was so very cold?
Sanders believes they formed directly from the dust drifting around the sun, along with radioactive aluminium-26 which was also readily available. The radioactivity provided the large amounts of heat required to melt dust and rubble as it accumulated. These planets of 50 to 100km across would form a frozen crust, helping to insulate the molten core, he explains.
A great advantage for Sanders’s hypothesis is that it removes the need for the unknown “zapping” mechanism in the conventional model. His ideas are finding more and more support in the scientific community, and recent dating of meteorites supports this alternative hypothesis.
So how did Sanders come to these new ideas? “This is an interesting philosophical observation of the way science works,” he says. “Anyone in science is curious and this goes back to the very beginnings of the solar system.”
His own interest began in 1993 when he got a letter “out of the blue” from a student eager to study meteorites – a field Sanders at that time knew little about. “I had to find out fast!” And so began his scientific journey to re-think how chondrules where formed.
“This was actually an old idea, that I thought was very plausible,” says Sanders. “Sometimes you have a hunch and if you’re lucky it’s supported by the data, otherwise you abandon it.” And in this case the data seems to back him up.
Sanders believes that a great advantage was starting out as an outsider in the field: “I was not blinkered by conventional thinking”. However, being an outsider he was keen to get his message out there. So he threw a party.
Every year about half of the 1,000 members of the Meteoritical Society get together for a scientific meeting. In 1998, five or six years into this research, Sanders hosted the meeting.
“I decided to give a really good party and ran the meeting in Dublin. There was a party every night. It was a turning point. As a newcomer on the scene, everyone now new who I was.”
A decade later, Sanders has just presented his latest findings at the 2009 Meteoritical Society, held in France last month, and his work was the subject of a recent article in New Scientist.
Now that his ideas seem to be gaining more and more acceptance in the scientific community, does Sanders think he will be famous for this work? “I think I’ll be more famous for running a good party in Dublin!”
Jeremy O'Brien is based at Bristol University and is on placement in The Irish Timesas a British Science Association Media Fellow