Astronomers know our solar system better than any other, but they are still learning new ways in which it does not seem to be particularly normal.
One of these oddities, in planetary-sized models, was the subject of a press conference held yesterday (January 8) at the annual meeting of the American Astronomical Society. The results could prompt scientists to review a fundamental theory of how the planets are formed.
And this, in turn, could have serious implications for the search for life outside our solar system. "The theory of planet formation is quite important even if you are only interested in habitable planets, because it is not enough to have a planet in the habitable zone, you must have chemicals consistent with life and a history consistent with the development of life" David Bennett , an astronomer of the University of Maryland, said at a press conference held during the meeting. "The better we can understand the formation of the planets, the better we will be able to predict which planets could be habitable". [7 Ways to Discover Alien Planets]
At the moment, the main theory of planetary formation, called the "core growth model", is adapted to explain what we see in our solar system ̵
Take, for example, the huge gap between Neptune and Saturn. Neptune is about 17 times the mass of the Earth, while Saturn is much larger at 95 times the Earth's mass, according to NASA. In the middle, nothing. The basic growth model explains this gap with a mechanism called "escaping gas growth".
Here's how the basic growth model explains the birth of a gas giant. First of all, pieces of rock and ice are grouped together, building what becomes a core – perhaps about 10 times the earth's mass. That nucleus has enough gravity to slowly grasp hydrogen and helium.
But under the pattern of escaping gas accumulation, once a developing planet has slowly brought together another 10 land masses or so of gas, something changes. The process becomes oppressive, with the planet quickly swallowing any other gases nearby until the source is exhausted.
If this idea is correct, explain the gap between Neptune and Saturn – Uranus and Neptune never hit the crucial dimensions to trigger escalating gas escalation, while Saturn and Jupiter have made and piled on huge masses.
There is only one problem: astronomers have realized that other solar systems are home to many planets of dimensions between these extremes, nicknamed sub-Saturni. An article published in December on The Astrophysical Journal Letters and presented at the meeting compared 30 different planets identified by a specific technique with what scientists expected to see based on the basic growth model. In that investigation, they found that the model does not correspond very well with reality.
This gives our solar system a strange quirk: sub-Saturnies are missing. "The lack of such planets in our solar system is more likely to be due to randomness or an accident," Bennett said.
And the lack of such planets in general is due to the fact that they are really difficult to detect. There is only one technique powerful enough to identify planets that orbit beyond what astronomers call "snow line", where loose material in a solar system is far enough from its sun light materials such as water can freeze – the kind of neighborhood you need to find sub-Saturn.
The technique, called gravitational microlensing, is based on a trick of the universe. When a very massive object passes exactly between an observer and a light source, its gravity removes the off course light, making it appear enlarged. If that massive object is a solar system, scientists can identify the planets by looking for small anomalies in the observations. [Exoplanet Discovery: The 7 Earth-Sized Planets of TRAPPIST-1 in Pictures]
But usually, they do not know much about the planet – just the feeling of how many times smaller it is of its sun. This is not the case with a sub-Saturn planet studied by many of the same researchers behind the research paper. In that case, they were able to define the mass of such a planet relying on a little patience, sharing the results in a second article published in December on The Astronomical Journal.
The team revisited a planet that had been identified by gravitational microlensing in 2012. From those early observations, the celestial geometry became agitated, taking the planetary system and the source of light that was magnifying out of alignment. The team was able to measure in an incredibly precise way how much the objects have been moved over the years from planetary identification, which they could then use to calculate an actual mass for the planet, called OGLE-2012-BLG-0950 .  That mass is in sub-Saturn prime territory, at about 39 terrestrial masses. That measurement firmly indicates a planet that can not resemble anything in our solar system. It is also a prowess in and of itself, the equivalent of identifying a dime from almost 70 miles (110 kilometers) away. "This is a really hard thing to do," said lead author Aparna Bhattacharya, an astronomer at NASA's Goddard Space Flight Center, during a press conference.
But it's not meant to be a one-off success, thanks to the expected Wide Field Infrared Survey Telescope, or WFIRST, which NASA is expected to launch in mid-2020. That tool will be able to use the same microlensing technique for identify and measure planets – and it will do so for hundreds of worlds so far. These measurements, in turn, could reveal other weaknesses in our understanding of how the planets are formed.