WFIRST will discover exoplanets in the center of the Milky Way. Distorted space-time will help him

The primary task of the WFIRST (Wide Field Infrared Survey Telescope) space telescope will be to look for extrasolar planets toward the center of the Milky Way, where most of the stars in our galaxy are located. By describing these planets, we will be getting to know better the different types of planetary systems in our galaxy.

When we combine planets discovered by WFIRST with those discovered by Kepler and TESS (Transiting Exoplanet Survey Satellite) telescopes, the first list of planets including planets of different masses moving in different orbits will end.

Most of the extrasolar planets discovered so far were discovered as they passed against the background of their host stars' shields, covering some of their radiation. The WFIRST telescope will also be able to record such transits, but by default it will look for exactly the opposite effect - small increases in the brightness of stars caused by the so-called microlensing. These types of phenomena are much rarer than transits, because they are based on a random alignment of two distant stars traversing space.

Microlensing phenomena caused by small planets are rare and short-lived, but are still stronger than those observed by other methods, "says David Bennett, who is gravitational microlensing at NASA Goddard Space Flight Center in Greenbelt. Since the probability of recording such a signal is one in a million, we need to observe hundreds of millions of stars to find low-massive planets using WFIRST.

Moreover, microlensing is a more effective method in searching for planets located in star ecospheres, i.e. in the range of distances from the star at which liquid water may potentially be on the surface of rocky planets.

Gravitational microlensing

This phenomenon occurs when the light passes near a massive object. Every object with mass bends the space-time that surrounds it. Light travels in space in a straight line, but if space itself is curved - e.g. near a star - light traveling in a straight line takes into account the bending of space-time.

Every time, when looking from our point in space, two stars pass very close to each other, the rays of light from the distal star bend passing through the curved spacetime near the closer star. If the stars literally pass one by one, the closer one acts like a natural cosmic lens, focusing and increasing the radiation intensity of the distal star.

Potential planets orbiting the proximal of both stars can also affect the lens light, acting like smaller lenses. Planetary deformations allow astronomers to measure the mass of these planets and the distance from the host star. That's how WFIRST intends to discover new planets.

Attempting to describe the population of planets in the Milky Way today resembles attempts to interpret half-covered images. To fully understand planetary systems, we must discover planets of all mass, orbiting at any distance from their stars. No single telescope will allow this, but when we combine the collections of planets discovered with WFIRST, Kepler and TESS, we will have a more complete picture - says Matthew Penny, assistant professor of physics and astronomy at the University of Louisiana at Baton Rouge.

Of the more than 4,000 planets discovered so far, only 86 were discovered by microlensing. Techniques currently used to search for other planets allow discovering planets completely unlike planets in the solar system. The transit method reveals the largest number of planets with a mass smaller than the mass of Neptune and orbiting closer to its star than Mercury. If we used the transit method on the Solar System, we would most likely not have noticed any of the eight planets.

The microlensing, which WFIRST will soon be looking for, will allow us to discover the analogues of each of the planets of the Solar System except Mercury, whose narrow orbit and low mass put it out of range of this telescope. WFIRST will, however, be able to find planets with a mass similar to that of Earth or less, and may also be able to discover large moons, such as Ganymede and Titan.

WFIRST will also discover planets from other under-explored categories. Microlensing is well suited for studying planets behind the star's ecosphere, such as Uranus and Neptune. Although there are only two ice giants in our planetary system, research indicates that they may be the most common type of planet in the Milky Way.

WFIRST will search where no one has searched yet

The Kepler Space Telescope searched for planets in an area of ​​100 sq. Degrees around 100,000 stars within about 1,000 light years. TESS searches the entire sky, tracks 200,000 stars, but only about 100 light-years away. In contrast, WFIRST will only analyze 3 sq. Sky, but will track 200 million stars at a distance of up to 10,000 light years.

As an infrared observing telescope, WFIRST will look behind dust and gas clouds that prevented other telescopes from searching for planets in the crowded central area of ​​the Milky Way.

Scientists estimate that a review of microlensing phenomena will allow us to discover another thousands of extrasolar planets, but also hundreds of other peculiar and interesting space objects: researchers will be able to discover objects that freely traverse space with a mass ranging from Mars to 100 solar masses. At one end of this range are planets ejected from their planetary systems due to interactions with gas giants. A bit further there are brown dwarfs, objects too big for planets, but not massive enough to become stars. Objects of this type do not shine like stars, but WFRIST will be able to see them in the infrared, because they emit residual heat remaining from the period of their formation. At the other extreme, there are neutron stars and black holes left after supernova explosions.

Brutal reality

The Budget Act 2020 provides funding for the WFIRST project until September this year. The budget proposal for 2021, however, includes a provision proposing the cancellation of WFIRST funding and focusing on completing the James Webb Space Telescope, whose launch (though unlikely) is currently planned for March 2021.



WFIRST will discover exoplanets in the center of the Milky Way. Distorted space-time will help him

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