Now, with the years of exoplanet-hunting for data in the bag, astronomers have made a new method of calculation and determined, there could be only 6 billion Earth-like planets orbiting stars like the Sun in the Milky Way.
“My calculations place an upper limit of 0.18 Earth-like planets per G-star type,” said astronomer Michelle Kunimoto of the University of British Columbia (UBC) in Canada. (You may remember that Kunimoto discovered a whopping 17 Kepler exoplanets in the data at very recently.)
“Estimating the frequency of different types of planets around stars can place significant constraints on the formation of planets and the evolution of theories, and help them optimize future missions dedicated to the search for exoplanets. ”
Our technology is improving, the number of planets outside the Solar System that we have found has increased by leaps and bounds. To date, we have confirmed 4,164, figure exoplanets, and the number continues to grow.
But it’s just a drop in the ocean compared to how many planets could to be there. There are an estimated 100 to 400 billion stars in the Milky Way, our galaxy, about 7 percent that are like our Sun: G-type main sequence stars.
However, most of the exoplanets we have found to date are large gas or giant ice, such as Jupiter or Neptune. Because it is incredibly difficult for us to see the planets directly, at very great distances, we are looking at the effects they have on their stars. The smaller, rocky planets like Earth and Mars are more difficult to find because their effects are much smaller, with much less signal-to-noise.
So it’s pretty plausible that there are a lot more Earth-like exoplanets in our galaxy than we’ve seen so far. To account for these missing planets, the team used a technique known as forward modeling to simulate data based on model parameters, applying it to a catalog of more than 200,000 stars. studied by the planet Kepler-hunting spacecraft that operated from 2009 to 2018.
“I started by simulating the entire population of exoplanets around wanted Kepler stars,” Kunimoto said.
“I marked each planet as” detected “or” missed “, depending on how likely it was my planet search algorithm would have found it. Then I compared the detection of planets to my catalog of planets. If the simulation produced a close match, then the initial population was probably a good representation of the actual population of the planets orbiting these stars. ”
From this approach, Kunimoto and his colleague UBC, astronomer Jaymie Matthews, could estimate the number of Earth-like planets in the Milky Way. They defined these between 0.75 and 1.5 times the mass of the Earth, orbiting a G-type star at a distance between 0.99 and 1.7 astronomical units (AU, the distance between the Earth and the Sun).
At the upper limit of the G-type estimate of stars in the galaxy, which is also very difficult to determine, these calculations returned a maximum of $ 6 billion from these exoplanets.
The actual number, of course, could be much smaller. And there is no guarantee that these planets have life, or are still habitable; after all, the planet Mars is 1.5 AU from the Sun, and it’s so empty of life there aren’t even any twirls.
But the number gives a new working tool, both in our search for this class of planets, and for the understanding of our own existence, in this old big part of space.
The research was published in The Astronomical Journal.