What are the methods used by astronomers to detect planets

Astrometry is the process of precisely tracking the trajectory of a star in the sky to determine the location of the planets that are gravitationally dragged by it. This is similar to the principle of the radial velocity method, except that astrometry does not involve Doppler shifts in stellar light.

This is a new means added to the "technology library" of human space exploration. As a new research method, it directs astronomers to focus on changes in the brightness of stars due to planetary motion, whose gravitational pull causes a relativistic effect that causes the photons that make up light to "pile up" in the form of energy and concentrate on the direction of the star's motion.

This method is particularly useful for discovering planets orbiting pulsars. Pulsars are extremely dense stars formed from the remnants of a star after its demise. It emits strong pulses as it rotates at high speeds – and because a pulsar's rotation is inherently stable, this radiation is very regular because of its rotation.

The biggest feature of this method is called "self-explanatory" - no complicated calculations are required, just use a powerful telescope to directly take a "passport" of a distant planet, and also obtain its "planetary passport" - which contains the planet's luminosity, temperature, atmosphere and orbit information.

Gravitational lensing is a method used by scientists to look for planets by observing the phenomenon that occurs when a huge star passes by the front side of a star from Earth. This is the only method capable of detecting Earth-sized planets around ordinary main-sequence stars.

This is by far the most productive method of confirming planets.

The clue found by the radial velocity method is the small fluctuations caused by the influence of the satellite planet when the parent star moves far and near relative to the Earth. Although the variation is small, it is possible to detect speed changes as low as 1 meter second using modern spectrometers. This method is often referred to as the "Doppler effect" because it measures changes in the gravitational drag of a star's light.

The basic principle of transit is to observe subtle changes in the brightness of a star as a planet crosses or passes through its surface. It has the advantage that the size of the planet can be determined from the light curve.

Generally, the occultation method is used, and the luminosity of the star decreases when the planet passes by the star, and the planet is judged by detecting and analyzing this photometric change.

Another, less common, is the use of planets orbiting to produce a regular Doppler effect in the spectrum of their host star.

Exodus detection methods are not included (Standard Model method). Methods of detecting exoplanets: astrometry.

The earliest method used to search for exoplanets was to determine the location of planets dragged by the force of the trigger by accurately measuring the trajectory of stars. The advantage of astrometric methods is that they can calculate the mass of traveling stars more accurately, and they are particularly sensitive to planets in large orbits.

However, the accuracy required for this method is very high, requiring years or even decades of observation to confirm the results. HD176051b, discovered in October 2010, is the only exoplanet that has been confirmed to date by astrometric discovery.

However, hopes are pinned on the launch of the European Space Agency's Gaia space astrometry satellite project in December 2013. Not long ago, the project published the second batch of scientific data. Gaia has measured the brightness, spectral signatures, three-dimensional positions and motions of more than 1 billion stars, and has created the most accurate three-dimensional star map of the Milky Way to date.

The researchers estimate that the new astrometry is expected to help them find tens of thousands of new exoplanets.

Here's how to probe:

1. Astrometry.

Astrometry is the earliest method of searching for exoplanets. This method is to accurately measure the position of a star in the sky and observe how that position changes over time.

If the star has a planet, the planet's gravity will cause the star to move in a tiny circular orbit. In this way, the stars and planets revolve around their common center of mass (the two-body problem). Since the mass of a star is much larger than that of a planet, its orbit is much smaller than that of a planet.

2. Radial velocity method.

Similar to astrometry, radial velocity takes advantage of the fact that a star moves in a tiny circular orbit under the influence of planetary gravity, but the goal is to measure the speed at which the star moves towards or from the Earth. According to the Doppler effect, the radial velocity of a star can be deduced from the movement of the spectral lines of the star.

3. Pulsar timing.

Pulsars are super-dense neutron stars that remain after supernovae**. As they rotate, pulsars emit very regular electromagnetic pulses, so slight anomalies in the pulses can show the movement of the pulsar. Like other planets, pulsars move under the influence of their planets, so the properties of their planets can be estimated by calculating their pulse changes.

4. Transit method.

The mass of the exoplanet can be estimated using the above method, and the diameter of the planet can be estimated by the transit rule. When a planet passes between its parent star and the Earth (i.e., transit), the luminosity of the parent star visible from the Earth decreases slightly. The degree of luminosity degradation is related to the size of the parent star and planet, for example, in HD 209458 luminosity decreases.

5. Gravity microlensing method.

Gravitational lensing is a type of gravitational lensing, in which the gravitational field of a star causes the light path of another distant star to change, resulting in a lens-like magnification effect, which only occurs when two stars and the Earth are almost in a straight line.

Because the relative position of the Earth and the stars is constantly changing, this lensing event lasts only a few days to a few weeks. Over the past decade, more than 1,000 gravitational microlensing phenomena have been observed.

6. Stellar disk method.

Many stars are surrounded by a stellar disk of dust, which absorbs the star's light and emits infrared rays, so it can be observed. Even if the total mass of dust is less than that of the Earth.

Their total surface area is still sufficient to reflect observable infrared light. The Haber Space Telescope can observe this dust through its near-infrared camera and multi-object spectrometer, while the Spitzer Space Telescope can receive a wider infrared spectrum for better images. More than 15% of the stars in the vicinity of the solar system have been found to have dust disks.

7. Direct photography.

Because planets are very faint compared to their parent stars, they are generally obscured by the light of their parent stars, so it is almost impossible to find exoplanets directly. But in some special cases.

Modern telescopes can also directly obtain images of exoplanets, such as those that are very large (significantly larger than Jupiter), have a large distance from their parent planets, and are relatively young (hence the higher temperatures and emit intense infrared rays).

Mercury: Mariner 10, Courier.

Venus: Dozens.

Mars: Dozens.

Saturn: Pioneer 11, Voyager 1, Voyager 2, Cassini.

Jupiter: Pioneer 10, Pioneer 11, Voyager 1, Voyager 2, Galileo, Juno.

Uranus: Voyager 2.

Neptune: Voyager 2.

Pluto: New Horizons.