synonymHD 209458 b(HD 209458b) Generally refers to HD 209458b
HD 209458b is an exoplanet orbiting the star HD 209458.It is located inPegasusDirection, about 150 from the earthLight year, for oneHot Jupiter。Around aSun like starfunction.The atmosphere on the surface of the planet is slowly boiling and vaporizing, resulting in very high temperature on the surface of the planet.This temperature can reach about 1500 degrees Celsius. The heated and ignited hydrogen makes the oxygen and carbon molecules on the planet peel off. These oxygen and carbon molecules are carried to form a flowing halo at the end of the planet.By observing this "blowing" effect, astronomers believe that this planet belongs to a new concept - the solid debris core forms this hugeGaseous planet。
HD 209458Apparent magnitudeGrade 7, invisible to the naked eye, availableBinocularsTo observe.The unofficial name of the planet is Osiris.The orbit radius of the planet is about 7 million kilometers, equal to 0.05 astronomical units, equivalent to one eighth of the orbital distance of Mercury.Its revolution period is 3.5 days, and the temperature on the side facing the star is about 1500centigradeAnd the back is only a few hundred degrees.quality220 times of the Earth, equal to 0.7JupiterQuality.
HD 209458b has the first record of multiple exoplanets, including the firstTransitThe exoplanets discovered by observation, the first known atmosphere, the first observed hydrogen layer in evaporation, and the atmospheric components containing oxygen and carbon.
Chinese name
HD 209458b
Foreign name
Osiris
Classification
planet
Discovery time
1999
Quality
1.33 × 10 ^ 27 kg, 227 ± 5 times Earth mass, 0.714 ± 0.017 times Jupiter mass
Average density
0.272 ± 0.007 times the density of Jupiter
Diameter
196477 km（±1258）
surface temperature
1043℃、1909°F、1316K
Apparent magnitude
7 etc
Right ascension
22h03m09s
Declination
+18°53′04″
Distance from ground
153.3 light year, 47 second gap, 1.450 × 10 ^ 15 km
Through the spectral observation of HD 209458, the planet was first discovered on November 5, 1999.Astronomers observed the luminosity of stars with known planets, hoping to measure the phenomenon that the transits of planets caused a slight decrease in luminosity.To make transit observation on the earth, the orbit tilt of the planet needs to enable the planet to pass between the earth and the star. At that time, no outer planet was found by transit observation.
On November 7, astronomers recorded that the brightness of the star fell by 1.7%, and it was later confirmed that it was caused by a planetary transit.Each transit lasts about 3 hours, and 1.5% of the star surface is covered by planets.
Hipparcos satellite has observed the star for many times, so that astronomers can accurately calculate the orbital period of the planet as 3.524736 days.The planet was suggested as the god of Hades in Egyptian mythologyOsirisTo name.
Physical characteristics
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HD 209458b
By analyzing the spectral data, it is concluded that the planet's mass is smaller than Jupiter's, about 0.7 times of Jupiter's.The planetary transit that can be observed on the Earth allows astronomers to calculate the radius of the planet, which is about 35% longer than Jupiter. This is impossible to do on an exoplanet discovered by Doppler detection alone.The reason why its radius is longer than that of Jupiter is that some people think that it is very close to the star, which can be called hot Jupiter. Its material expands at high temperature, resulting in its low density.
Planetary atmosphere
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Hydrogen tail
On November 27, 2001, through spectral analysis, the Hubble Space Telescope found that the planet's atmosphere contained the element sodium, which was the first time that people found the atmosphere on an outer planet. By 2003/04, astronomers had found hydrogen, carbon and oxygen in the atmosphere, and the temperature could reach 10000 degrees Celsius.Under this high temperature, the particle velocity is distributed in the form of a Maxwell Boltzmann distribution, and the particle velocity at the tail is higher than the escape velocity of the planet.It is estimated that the planet is losing 1-5 billion kilograms of hydrogen per second, and its hydrogen tail can reach 200000 kilometers in length.
Planetary environment
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Tidal locking
HD 209458b is 150 light-years away from the Earth. This is a hot Jupiter. The convenient condition of this planet is that you don't have to worry about setting the time of your watch.
HD 209458bTidal locking （tidally locked）, which means that one side of the planet will always face the main star, and the other side will always be in darkness.
Due to this inconsistency, the wind force of the planet is similar to that of HD189733b, but the wind speed is only 4500 miles per hour.[1]
Black snow
It's amazing to wake up and find the earth covered with snow!But there is no such romance on exoplanet HD 209458b, where hot black snow falls and the earth resembles the forest after fire.
Titanium oxide snow falls on exoplanet HD 209458b[2]
Exoplanet HD 209458b belongs to“Hot Jupiter”Family, "hot Jupiter" is a kind of giant gaseous planets very close to its parent star.In contrast, Jupiter and Saturn, the giant gas planets in our solar system, are cold because they are far away from the sun.HD 209458b is still locked by tide（tidally locked）That is to say, one side of the planet is always in the day, while the other side is always in the night.The temperature of the day side is as high as 2000 ℃, while the night side is relatively low, about 500 ℃.
Of course, on such a planet, snowflakes cannot be formed by condensation of water!Due to the huge temperature difference between the two hemispheres, the atmospheric circulation constantly exchanges matter and energy between the two hemispheres.This means that some substances are in a gaseous state on the day side, while those flowing into the night side will be cooled into solid and fall in the form of "snowflakes".One of them is called titanium oxide.
Although titanium oxide is only a small part of hot Jupiter's atmosphere, this compound has unique properties that can form snow.Old models of hot Jupiter show that titanium oxide condenses into snowflakes and falls in the night sky, and then accumulates on the ground forever.Vivien Parmentier, a French scientist, said: "It can be imagined that if there is no mechanism to make snowflakes become water vapor again on the earth, there will be no snow."
Scientists have created a new computer 3D model to simulate the changes in the state of matter on Hot Jupiter.The new model shows that the falling solid titanium oxide can be turned into gas again and enter the atmosphere, and the strong updraft can bring it into the upper atmosphere.Titanium oxide entering the upper atmosphere can participate in a new round of snowfall, thus forming a continuous material cycle.[2]
