Michel Mayor (Michel Mayor) found a extrasolar planets orbiting sun-like stars, and in our understanding of cosmic evolution and the earth made many contributions to place in the universe.He and Didier queiroz (Didier Queloz) professor won the 2019 Nobel Prize for physics.

Can you imagine that somewhere in the universe there may be other forms of life?At first, the idea seemed fanciful or difficult to understand.However, as an astrophysicist, I can tell you, this is actually quite possible.Why is that?Because there are so many planets in the universe, unimaginable number, some of the conditions of the planet might be good for life.Before discussing the possibility of other life in the universe, let's look at how we find planets outside the solar system.

How to explore the habitable planets

Looking for may be the best of our knowledge of the forms of lifeHabitable planetsWe're looking for is similar to the earth.A necessary condition is that these planets should be around a radiation heat and light of stars.The star can offer the right temperature for the development of life and energy production conditions, like the sun on the earth.But, when a dim planet, such as the earth next to a bright star (for example, when the sun), scientists cannot directly detect the planet, because the reflected light is bright star light.For example, the brightness of the sun than each planet circling it one billion times the reflection of light are higher.Therefore, we need to develop an indirect method to detect the existence of the planet.One method involves testing the planet motion velocity caused by the change of nearby stars.To understand this method, we must be familiar with the two concepts - spectral lines and the doppler effect.

Spectral lines

As you may know, every atom energy level and its corresponding around the nucleus electronic movement.When the light through a atom, and atomic energy level corresponding to specific wavelengths of light is absorbed by atoms, and then atoms emit light spontaneously, but the frequency and the frequency of the absorbed light is slightly different (i.e., the offset).Each atom (iron, hydrogen, calcium, etc.) of migration are specific.This means that if we are able to detect the interact with atoms emitting light, after the analysis of its wavelength, can get the specific "fingerprints" of the atom.Spectrum is continuous before interact with atoms, and detect the spectrum can see less of a particular wavelength (dark) or enhance (on line).These lines are calledSpectral lines¹.

Distant planets spectral lines

Each star has a specific combination of atoms in the atmosphere around.So, by detecting light through the star's atmosphere, we can get its unique spectral fingerprints, this is the star of all kinds of atoms in the atmosphere.We can use these spectral lines on the tiny deviation to infer the existence of a planet orbiting the star.These small offset is caused by the doppler effect.

The doppler effect

Have you ever noticed that when an ambulance horns coming toward you, alarm tone changes, it is coming towards you tone becomes more and more sharp, tone becomes lower, more soft when they leave?In fact, the sound of sirens has not changed.Change is when the ambulance is close to you, every sound waves to reach your time shorter than the previous acoustic, lead to the increase of the frequency of sound waves.This makes the siren gasping when close to you, flattens out when away from you²(Figure 1).Known as the observed frequency changeThe doppler effect.

Any type of wave is follow the law, including light.So when objects like stars shine while moving towards us, its spectrum will be to short wavelength, high frequency mobile (called blue shift), and when it is far from us, will move toward the long wavelength, low frequency spectrum (called red shift).When planets around stars, gravity will influence the movement of the stars of the planets - stars along the elliptical orbit motion caused by the planetary orbits, so the star to earth moving, sometimes sometimes far away from the earth.Star direction relative to the earth changes will cause changes in the spectral lines³.In general, this means we can by measuring the doppler shift of the spectral line star, indirectly infer the existence of the orbits of the planets (Figure 2).

Cross-correlation technology

Using the doppler effect to detect the presence of unseen planet, is a big challenge.Caused by changes in the rate of exoplanets only a few meters per second, or even smaller.Such a tiny change means, star of spectral doppler frequency shift is less than one over one billion of its emission wavelength (1/1000000000) [1].This is a very small change, only by a spectral doppler frequency shift is unable to accurately measure.

So, how can we improve the precision of the measurement?We use another clever technique, calledCross-correlation technology.The technology in the 1980 s and 90 s has been optimized, in detecting extrasolar planets we have played an important role.

Key idea of this technology is that, when stars of interest measurement, we not only focus on a line of migration, but pay attention to the doppler effect caused by the collective migration of all lines.To this end, we use the equipment (called CORAVEL spectrometerFigure 3. A) [1,2].CORAVELThe spectrometerIn a perforated plate (Figure 3 b), located in the hole we expect from a specific light of the stars in the dark line position.All of the transmitted light through these holes are sent to a detector.When the dark line of stars is just located in the front of the hole, we detect the transmitted light (at leastFigure 3 c, left).If, however, because of the exoplanets has affected the movement of the stars and the doppler frequency shift, so relative to the position of the hole on the board, tens of thousands of spectral line of position will move at the same time, through the hole will increase the amount of transmitted light (Figure 3 c, right).After the doppler frequency shift, we need to move the tablet, the hole again and dark line alignment, this detector to detect the transmission of light and will change to a minimum.

Therefore, by measuring the two stars in its orbit position absorption spectral lines, and mobile tablet twice to detect the amount of light is changed to a minimum, we know the tablet in the first minimum (stars of the first position) and the second minimum value (the second position of the stars) to move between how much.It is because of the existence of exoplanets that causes stars spectral doppler frequency shift occurs, we observe the tablet to transfer between two dark spectrum.By counting stars spectral doppler frequency shift, combined with other measurements, we can understand the characteristics of detecting exoplanets.

Cross-correlation technology allows us to put all from separate spectral doppler frequency shift information aggregation in a single physical quantities.The physical quantities is calledDoppler velocity, because it can be said by near the planet's existence and cause changes in the rate of star.Using the doppler speed, combined with other measurement, we can not only deduce the existence of the planet, you can also know its quality, size, and orbits the time needed for a week.In 1995, my colleagues and I Didier ⋅ queiroz (Didier Queloz) using this technique found pegasus 51 b - this is the first discoveredexoplanets[3].

Pegasus 51 b: discovered the first orbiting sun-like stars movement of exoplanets

Pegasus 51 b (Figure 4 a) is a about 50 light-years from earth (about 47 trillion km!)Planet, pegasus in the Milky Way⁴.It's temperature is very high, about 1000 degrees Celsius.It is orbiting a star called the pegasus 51 sunlike stars, orbits about 4.2 days.Pegasus 51 b is mainly composed of gas and classified as a gas giant planets like Jupiter.Because its orbit is very close to the stars, it is sometimes referred to as' hot jupiters'.The quality of the pegasus 51 b is about 47% lighter than Jupiter, 50% volume is larger than Jupiter.Pegasus 51 stars heavier than our sun is about 11% and 23% larger volume.

As mentioned earlier, pegasus 51 b is discovered the first extrasolar planets orbiting stars.This star and exoplanets itself is of great research value, and this finding also brought two breakthrough to planetary exploration field.

First, after scientists are not sure, whether in the universe except outside the solar system planets orbiting stars still exist, pegasus 51 b findings demonstrate that such planets exist, and can be detected using cross-correlation technology.

Second, it proves that the called a planetary migration hypothesis, namely with the passage of time, the planet can happen displacement, surrounded by a closer to their stars⁵.For astrophysicist, that's very close to their star around the giant planets very attractive, because they can more quickly using cross-correlation technique were observed.Before found pegasus 51 b, scientists believe that the giant planet's orbital period cannot be less than 10 years, this means using the doppler effect to detect a planet needs 10 years!But our findings suggest that the planet's orbital period may be as little as a few days, only one over one thousand of the expected!This means that some exoplanets could be detected within a few days.

Both breakthrough has greatly promoted the more the orbits of exoplanets detecting.Now, scientists have found more than 5000 such planets!This is in search for possible life is an important step in the universe.

Life in the universe

We currently includes three main features: the definition of life life system should be able to protect themselves is not affected by the environment, can interact with the environment, and the information passed on to the next generation.This kind of information transfer is through the long atoms and molecules chain (called genetic material or DNA), and the material is very fragile.The DNA molecule needs specific temperature and moisture.This means that if there was life on an exoplanet, it must meet these environmental conditions⁶.As a result, how likely it is that find such a planet?Well, since there are so many planets in the universe, we absolutely can be sure, many of these planets has the possibility that life evolved.But, as scientists, we are not content to simply say 'yes, probably' - we want to prove it directly.

To find life on other planets, the simplest method seems to be to the launch of the spacecraft, look around and take pictures.But, to our current technology and understanding of physics, this is impossible, because the spacecraft to the very distant planets take too long, spend a lot of energy⁷.Therefore, we need to use the remote detection method, through indirect measurement and observation to determine whether there is life on a planet.For example, you can use the spectrum to analyze exoplanets chemical composition of the atmosphere.Because we are very familiar with oxygen in the earth's atmosphere (ozone), nitrogen, methane and carbon dioxide and other chemical composition of the line, we can try to find a similar on other planets atmosphere of the spectrum⁸.This method and other research methods, although very promising, but is very complicated, need to be improved to play a role.Therefore, whether and how to detect exoplanets life on this important issue, for the next generation of young scientists like you is still a great challenge!

Advice to readers

I believe that to become a scientist, you need to have very strong curiosity.Science is not a "normal" job, it's not just for the money.However, if you are curious for any problems in the scientific, I believe that as a scientist you'll enjoy it - it's as simple as that.I never regret chose to become a scientist.For me, as one of the joys of a scientist, was lucky enough to work with people from all over the world.This feeling in many parts of the world are friends.

I also think that to scientists, is good at teamwork is very important.For years, I have led a few research team, I found that even if only one person and teamwork is poorer, the whole team will be adversely affected.As a member of the team, you should get along well with colleague, and willing to work together with them.Therefore, to ensure that partner with the right people, and enjoy everyday interactions.

Further reading

• Michel Mayor, the Nobel Prize in Physics 2019: Official interview (Nobel Prize).
• The 2019 Nobel Prize in Physics - The discovery of The first exoplanet (Nobel Prize).

The vocabulary

Habitable planets (Habitable Planet):writeMeet life necessary condition for the survival of the planet.

Spectral lines (Spectral Line):write, a specific wavelength of light emitted by the atomic absorption or.

The Doppler Effect (Doppler Effect):writeA bundle of wave measurement wavelength (frequency) and subject to change with its source toward or away from the observer's physical effect.

Cross-correlation technology (Cross - Correlation Technique):writeA use of doppler effect of the influence of the spectral lines from distant stars method to detect a planet outside our solar system.

Spectrometer (Spectrometer):writeA device used to detect and analyze the spectrum, we use it to analyze from the outside is the light of the stars and planets.

Doppler Velocity (Doppler Velocity):writeClose to the planet's existence caused by changes in the rate of stars.

Exoplanets (Exoplanet):writeLocated in the planets outside the solar system.

Conflict of interest statement

The author statement, the study is in no may be interpreted as potential conflicts of interest under the condition of commercial or financial relationships.

Thank you

Thank you forNoa SegevInterview and participate in the writing of this article.Thank you forSharon Amlani 提供的Figure 1,Figure 2,Figure 3 c.Thank you ' ' ' 'the very public, and the translator Zhao Jinyu, Maya blue contribution to Chinese translation in this paper.

footnotes

1.writeClick here to learn more about the ray of light.

2.writeClick here to learn more.Figure 1Are related in some explanation.

3.writeClick here to watch the video.

4.writeClick here to learn more.

5.writeClick here to learn more knowledge about the planet.

6.writeEven if meet the conditions, does not necessarily mean that there is life on the planet, but there is the possibility of the existence of life.Outside our cognitive, there may be different forms of life, not familiar with the environment in which we live.But due to the level of science and technology limited, we start with the easiest place to start.

7.writeThis also means that even if we find a suitable for human living planet outside our solar system, at the current development level of physics, humans are not suitable for moving to the planet.Therefore, we need to do our best to protect the earth, many future generations of people are going to live here.

8.writeIf you want to learn more knowledge about this method, you can read this article [4].

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reference

[1]writeMayor, m. 2020. Nobel section: the plurality of worlds in the cosmos: a dream of antiquity, and a modern reality of astrophysics.Rev. Mod. Phys.92:030502. Available online at:https://journals.aps.org/rmp/abstract/10.1103/RevModPhys.92.030502

[2]writeBaranne, a., Mayor, m., and Poncet j. l. 1979. Coravel - A new tool for radial velocity measurement.Vist. Astron.Remove 9-316 doi: 10.1016/0083-6656 (79) 90016-3

[3]writeMayor, m., and Queloz, d. 1995. Jupiter - A mass companion to A solar -type star.Nature378:355-9.

[4]writeSchwieterman, e. w., Kiang, n. y., Parenteau, m. N., Harman, c. e., DasSarma, s., Fisher, t. m., et al. 2018. The Exoplanet biosignatures: a review of remotely detectable signs of life.Astrobiology. To survey 63-708. Doi: 10.1089 / ast. 2017.1729