Life A chance to look back in time: Birth of a solar system just like ours
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A chance to look back in time: Birth of a solar system just like ours

Birth of solar system
Is this what our solar system looked like in its early years, as the planets were beginning to form? Photo: ALMA/Tomoyuki Kudo
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Astronomers only have theories to explain how the solar system – Sun, planets and asteroids – was formed.

One problem is that what’s required to make a rocky planet like Earth is different to what’s required to make a gas giant, such as Jupiter, Saturn, Uranus or Neptune.

The question is so complex that we’d almost need to travel back in time and watch our corner of the universe give birth to itself.

Impossible, right? Maybe not

Japanese astronomers, in a new paper, have identified the formation sites of planets around a young star resembling our Sun, and “suggest that we are witnessing the formation of a planetary system similar to our own”, according to a statement from the National Institutes of Natural Sciences in Tokyo.

The star, DM Tau – about 470 light years away, and located in the Taurus constellation – has been a subject of interest for some years because of a giant ring of dust encircling it.

This ring has led to two competing theories: That an asteroid field was in formation or already had formed; or that a planet was under formation with an orbit equivalent to that of Neptune.

The ALMA telescope complex on the high plateau of Chile is capable of seeing the birth of stars through dust clouds. Photo: NASA

Now Tomoyuki Kudo, an astronomer at the National Astronomical Observatory of Japan (NAOJ), has solved the argument using the Atacama Large Millimetre/submillimetre Array (ALMA) – a telescope complex that NASA describes as “the most powerful Earth observatory in history”.

Located on the Chajnantor Plateau, at an altitude of 5000 metres in the Chilean Andes, ALMA is capable of examining events and objects that “are difficult to see in visible wavelengths, such as planetary systems under construction, which are usually obscured by clouds of dust”, according to space.com.

In this instance ALMA revealed there are actually two separate rings around DM Tau – not just one.  

“Previous observations inferred two different models for the disk around DM Tau,” Dr Kudo said.

“Some studies suggested the radius of the ring is about where the solar system’s asteroid belt would be. Other observations put the size out where Neptune would be. Our ALMA observations provided a clear answer: Both are right. DM Tau has two rings, one at each location.”

A bright light amidst the dust

The researchers found a bright patch in the outer ring. This indicates “a local concentration of dust, which would be a possible formation site for a planet like Uranus or Neptune”.

About half the mass of the Sun and estimated to be three to five million years old, DM Tau will considerably increase in mass over the coming millions of years. The rings of matter may resolve themselves into something more complex, giving birth to more planets and other objects.

“We are also interested in seeing the details in the inner region of the disk, because the Earth formed in such an area around the young Sun,” Jun Hashimoto said, a researcher at the Astrobiology Centre, Japan.

“The distribution of dust in the inner ring around DM Tau will provide crucial information to understand the origin of planets like Earth.”

In this illustration, several dust rings circle the sun. These rings form when planets’ gravities tug dust grains into orbit around the Sun. Image: NASA’s Goddard Space Flight Centre

Meanwhile, we are making new and surprising discoveries much closer to home. Two new studies report discoveries of dust rings in the inner solar system.

Solar scientists at the Naval Research Laboratory in Washington DC used NASA data to describe a fine haze of cosmic dust over Mercury’s orbit, forming a ring some 24 million kilometres wide.

Dust to dust

Mercury – which could be circled in five hours in a plane ride – wades through this vast dust trail as it circles the Sun.

Ironically, the scientists Guillermo Stenborg and Russell Howard stumbled upon the dust ring while searching for evidence of a dust-free region close to the Sun.

“We found it by chance,” Dr Stenborg said, in a statement from NASA/Goddard Space Flight Centre.

A second study from NASA identifies the likely source of the dust ring at Venus’ orbit: A group of asteroids never seen before, co-orbiting with the planet.

“It’s not every day you get to discover something new in the inner solar system,” said Marc Kuchner, an author on the Venus study and astrophysicist at NASA’s Goddard Space Flight Centre in Greenbelt, Maryland.

“This is right in our neighbourhood.”

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