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Find out exactly the masses of planets outside the solar system

After more than 300 planets outside the solar system have already been discovered, Shai Zucker, from the Department of Geophysics and Planetary Sciences at Tel Aviv University, says that it is worth performing astrometry tests - the movement of stars against the background of the sky to know the mass of the planets in their systems * Zucker gave a lecture as part of the annual space conference

Empty artist's impression of planets orbiting a distant star similar to our sun.
Empty artist's impression of planets orbiting a distant star similar to our sun.

The annual space conference that took place last week at the Air Force Base in Herzliya, was mainly concerned with the technologies of launchers and satellites, but nevertheless there was one scientific lecture. Dr. Shai Zucker, from the Department of Geophysics and Planetary Sciences at Tel Aviv University told about his research in the relatively new field - the study of planets outside the solar system

"Why are we looking for planets outside the solar system? Until 1995 we only had one example of a solar system. our solar system where the orbits of the planets are elliptical, and all more or less in the same plane; All the planets orbit the sun in the same direction, and they are also divided into two main populations: terrestrial planets with rocky soil, and fair planets - gas giants, and in addition to them there is another diverse population of comets, asteroids, dust, gas.

From the only example of the solar system, we developed a model that begins with the formation of a star - a cloud of gas and dust that at some stage, due to various reasons of inhomogeneity in certain places, begins to pull the material around and we begin to see that the gas connects to a kind of disk with a denser sphere in the center, which eventually becomes the central star (the sun ) and the surrounding gas and dust crystallize into planets, comets and asteroids. This is still the model that is being talked about, but it has been updated a bit, after predictions derived from it did not hold true in the new solar systems.

The question arises why did we have to wait until the nineties of the twentieth century to discover planets? The light intensity from the planets is billions of times smaller than the light intensity of the star. From a distance of about 30 light years, the distance from us to the system is hundreds of thousands of times greater than the distance between the star and the planet. It is clear from this that we had to rely on indirect methods to discover the planets.

Doppler effect

The first method was to use the Doppler effect to find the planet. The basic idea is that the attraction between the star and the planet is mutual. The planet rotates in an elliptical orbit due to the pull of the star. It attracts the star, so the star will also arrive in an elliptical orbit but much smaller. Doppler effect, in one sentence: when a source of waves moves towards us - the frequency that was received is higher than the one that it emitted. Even when he moves away from us it will be lower. You can measure the speed according to this effect and this is how the police radar works."

Each star has its own spectrum and reflects its characteristics. The central feature in the star's spectrum is the series of absorption lines. As the star moves away from us, its spectrum is shifted toward the red. (lower frequencies) and that as it approaches us the spectrum is shifted to the blue.

The first planet that was discovered by the latest means - in 1995 Pegasi 51B, was a big surprise. This is a huge planet - at least half the mass of Jupiter. And it is very close to its mother star - its cycle time is four days. In this he contradicted all the old theories about the formation of the solar system.

Searching for planets using the eclipse method

The method by which we discovered the first planet, the Doppler method, tells us what the mass of the planet is, how close it is to the star. But not for example what are the conditions on the surface of the planet and its radius. The other possible method is to search for planets through eclipses. There is a certain chance that during the orbit the planet hides part of the star, that is, it eclipses the star. The problem is that you can't see the tiny dot moving across its sun because it's just too far away. What we see is that the star's light will weaken slightly during the eclipse. The first planet discovered using this method is  HD209458b . We actually discovered it in the usual way at the end of 1999 but we also discovered in addition that it performs this eclipse. For two hours you see a decrease of one and a half percent in the intensity of the light coming from the star. So it was the holy grail of the field. The eclipse made it possible to measure the density of the planet and the force of gravity on its surface, and all this without seeing it itself. To date, about 50 such planets are known. Some are even closer to their sun than 51 Pegasi B.

Lately there has been a development in a new direction thanks to these planets making eclipses, information we are getting about the atmospheres Not only physical conditions but also chemical ones. It all started with the measurement of absorption in the atmosphere of HD209458b.

So far we have found sodium, carbon, oxygen, carbon, water vapor, methane, and even carbon dioxide. A measurement made from the Spitzer Infrared Space Telescope allowed us to look at a planet even when it is behind the star. And so we saw how much light was emitted in infrared and that tells about their temperatures.

In the last few weeks even We managed to photograph one planet, but with this method we only manage to identify planets that are very far from their sun and large enough so that they have a lot of their own light.

What is expected in the future?

According to Zucker, the scientists want to try a third detection method "We would like to be able to perform another type of measurement - astrometry. See movement on the sky map. Using this method will resolve the ambiguity regarding the mass of the planets. However, in order to perform astrometry, devices with a much higher level of accuracy are required than those that exist today. For example, VLT - the very large telescope of the Southern European Observatory ESO in Chile, is a sort of array of four telescopes, each of which is eight meters in diameter. This array should start working as an interferometer and perform astrometric measurements with very high accuracy. In the distant future, finer observations will be made possible by a new type of telescopes ELT - EXTREMELY LARGE TELESCOPE. And here we are talking about a mirror with a diameter of several tens of meters.

And of course the best place to look at planets outside the solar system is from space. The atmosphere causes problems of light absorption and blurring. Therefore, photometric and astrometric measurements cannot reach sufficient accuracy. Today, there are plans to launch dedicated telescopes into space for these purposes

Satellite COROT The French, who has been in space for two years, and the American Kepler, which is scheduled to be launched in about a month, are looking for planets using the eclipse method. Both of them together will complete the picture for us regarding the planets making transits in front of their sun. For the more distant future we will be able to use the GAIA telescopes of the European Space Agency (launch planned for 2012) and the American SIM (launch date not yet known), both of which will search for the tiny movements in the sky (astrometry).

And even further, the American TPF and the European Darwin will conduct a direct search for Earth-like planets using interformatria. Darwin will actually be a constellation of several satellites.

In conclusion, Zucker says that after we discovered planets through the Doppler effect and through eclipses, we were excited by the latest innovations in the field, we were filled with anticipation for the next space missions that will benefit us. Now all that remains is to look for a life.

Previous reports from the 2009 Space Conference on the Knowledge website:

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