Proxima Centauri b facts for kids
An artist's idea of what Proxima Centauri b might look like. It is shown as a rocky planet, with its star Proxima Centauri and the Alpha Centauri system in the background. We don't know what the planet truly looks like.
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| Discovery | |
|---|---|
| Discovered by | Anglada-Escudé et al. |
| Discovery site | European Southern Observatory |
| Discovery date | 24 August 2016 |
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Detection method
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Doppler spectroscopy |
| Orbital characteristics | |
| 0.04848±0.00029 AU | |
| Eccentricity | low |
| 11.18465±0.00053 d | |
| Semi-amplitude | 1.226±0.062 m/s |
| Star | Proxima Centauri |
| Physical characteristics | |
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Mean radius
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0.94–1.4 R⊕ |
| Mass | ≥1.055±0.055 M⊕ |
| Temperature | Teq: 234 K (−39 °C; −38 °F) |
Proxima Centauri b is an exoplanet, which is a planet outside our Solar System. It orbits a red dwarf star called Proxima Centauri. This star is in the constellation Centaurus. Scientists also call this planet Proxima b or Alpha Centauri Cb.
Proxima Centauri is the closest star to our Sun. It is about 4.2 light-years away from Earth. This star is part of a bigger group of stars called the Alpha Centauri system. Proxima b is one of the closest known exoplanets to our Solar System. Another planet, Proxima d, orbits even closer to the star. Scientists are still studying a possible third planet, Proxima c.
Proxima Centauri b orbits its star much closer than Earth orbits the Sun. It takes about 11.2 Earth days to complete one orbit. This planet is likely a rocky world, similar to Earth. Its minimum mass is about 1.06 times that of Earth. Its size is probably a bit larger than Earth's.
The planet orbits in the "habitable zone" of its star. This means it could have liquid water on its surface. However, we do not know if it has an atmosphere. An atmosphere is very important for a planet to be habitable. Proxima Centauri is a flare star. This means it often shoots out strong bursts of energy. These bursts could strip away a planet's atmosphere.
The discovery of Proxima Centauri b was announced on August 24, 2016. The European Southern Observatory (ESO) confirmed its existence. They used a method called Doppler spectroscopy. This method measures how the star "wobbles" due to the planet's pull. Finding Proxima Centauri b was a big step in planetology. It made people more interested in the Alpha Centauri star system. Because it is so close, Proxima Centauri b is a great target for future robotic space missions.
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Discovering Proxima Centauri b
Scientists were looking for planets around Proxima Centauri even before Proxima Centauri b was found. Earlier studies in 2008 and 2009 did not find any large planets in the habitable zone. Planets are very common around dwarf stars. Many red dwarfs, like Proxima Centauri, have planets in their habitable zones. Red dwarfs are also the most common type of star in our galaxy.
Before 2016, telescopes in Chile noticed strange movements in Proxima Centauri. These movements could not be explained by the star's normal activity. This suggested that a planet might be orbiting the star. In January 2016, a group of astronomers started the "Pale Red Dot" project. Their goal was to confirm if this planet truly existed.
On August 24, 2016, the team announced their discovery. They confirmed that a rocky planet in Proxima Centauri's habitable zone caused the star's wobble. This planet was named Proxima Centauri b.
In 2022, another planet, Proxima Centauri d, was confirmed. It orbits even closer to the star. Scientists also found a possible planet called Proxima Centauri c in 2020. However, its existence is still being debated.
What is Proxima Centauri b Like?
Distance and Orbit
Proxima Centauri b is the closest exoplanet to Earth. It is about 4.2 light-years away. It takes Proxima Centauri b about 11.2 Earth days to orbit its star. This planet is very close to Proxima Centauri. It is over 20 times closer than Earth is to the Sun. Its orbit is quite circular, meaning it does not swing too far in or out.
Size and What It's Made Of
Scientists estimate that Proxima Centauri b has a minimum mass of about 1.055 times Earth's mass. This is a "minimum" mass because we do not know the exact tilt of its orbit. If we knew the tilt, its true mass might be closer to 1.44 Earth masses. This makes it similar in size to Earth.
The planet's exact radius is hard to know. Estimates suggest it could be between 0.94 and 1.4 times Earth's radius. Depending on what it is made of, Proxima Centauri b could be like Mercury with a big core. Or it could be a planet rich in water. Scientists study the elements in Proxima Centauri to guess what its planets might be made of.
Is It Tidally Locked?
Proxima Centauri b is probably tidally locked to its star. This means one side of the planet would always face Proxima Centauri. The other side would always be in darkness. This could create extreme climates. Only certain parts of the planet might be warm enough for life.
However, the planet might not be fully tidally locked. If its orbit is not perfectly circular, it could spin more. This spinning could cause strong ocean tides, much stronger than on Earth. It could also lead to more volcanic activity.
The Star: Proxima Centauri
Proxima Centauri is a red dwarf star. It gives off much less light and energy than our Sun. It radiates only about 0.005% of the visible light of the Sun. Even so, Proxima Centauri b receives about 70% of the infrared energy that Earth gets from the Sun. This is because Proxima Centauri b orbits very close to its star.
Proxima Centauri is also a flare star. Its brightness can change a lot in just a few hours. This means it sends out powerful bursts of energy.
The star is much smaller than the Sun. It has about 12.2% of the Sun's mass and 15.4% of the Sun's radius. Its surface temperature is about 3050 Kelvin. Proxima Centauri has a strong magnetic field. This field changes in a seven-year cycle.
Proxima Centauri is the closest star to our Sun. It is part of a multiple star system with Alpha Centauri A and Alpha Centauri B. These two stars form a binary star system. Proxima Centauri is too dim to see without a telescope, except during its powerful flares.
Conditions on Proxima Centauri b
Climate and Atmosphere
Proxima Centauri b is in its star's habitable zone. It receives about 65% of the energy that Earth gets from the Sun. Its average temperature is estimated to be about -39 degrees Celsius (-38 degrees Fahrenheit). Many things affect the climate of Proxima Centauri b. These include its orbit, the star's radiation, and how clouds behave.
Scientists have used computer models to guess what Proxima Centauri b's atmosphere might be like. If it has an atmosphere, it might contain oxygen and carbon dioxide. If the planet has a magnetic field, the star's activity could create auroras. These are like the Northern Lights on Earth.
Different scenarios are possible for the planet's surface. It could be partly or fully covered in ice. It might have planet-wide oceans or small seas. It could also be mostly dry land. Some models even suggest "eyeball" or "lobster-shaped" areas of liquid water near the equator. A hidden ocean under a thin layer of ice is also possible.
Keeping an Atmosphere
Keeping an atmosphere is a big challenge for Proxima Centauri b. This is due to several reasons:
- Strong Radiation: Proxima Centauri sends out a lot of UV radiation and X-rays. Proxima Centauri b gets 10 to 60 times more of this radiation than Earth. This radiation can heat up and strip away a planet's atmosphere. It can also break water into hydrogen and oxygen. The hydrogen can then escape into space.
- Stellar Winds: The star's stellar winds and coronal mass ejections are also a threat. These are powerful streams of particles from the star. They could be 4 to 80 times stronger than the Sun's stellar wind on Earth. These winds can push away a planet's atmosphere.
- Tidal Locking: If the planet is tidally locked, its atmosphere could freeze and collapse on the dark side.
- Early History: When Proxima Centauri was young, its habitable zone was farther out. If Proxima Centauri b formed in its current orbit, it might have been too close to the star for water to stay liquid. This could have caused a "runaway greenhouse effect." All its water would have turned to steam and been lost, similar to what happened on Venus.
Even if Proxima Centauri b lost its first atmosphere, volcanic activity could create a new one. This new atmosphere might have a lot of carbon dioxide. This could make it more stable. Also, comets hitting the planet could bring new water.
Could There Be Life?
When scientists talk about a planet being "habitable," they usually mean it could have liquid water on its surface. For life as we know it, liquid water and an atmosphere are usually needed. Life could exist deep under the surface, like in the oceans of Europa in our Solar System. But this kind of life would be very hard to detect from Earth.
Challenges for Life
There are many challenges for life on Proxima Centauri b:
- Star Activity and Tidal Locking: The star's flares and the planet's tidal locking make it hard for life to develop.
- Radiation: While UV radiation from Proxima Centauri is different from the Sun's, strong stellar activity could destroy an ozone layer. This would expose the surface to dangerous levels of UV radiation.
- Toxic Gases: Gases like oxygen or carbon monoxide could build up to toxic levels in the atmosphere. However, high oxygen levels might also help complex life forms to grow.
- Tides: If there are oceans, very strong tides could flood and dry coastal areas. This might help life to start. But extremely strong tides could also cause too much erosion and heating, making the planet uninhabitable.
On the bright side, red dwarf stars like Proxima Centauri live for a very long time. They live much longer than our Sun. This gives life plenty of time to develop. The light from Proxima Centauri is not ideal for oxygen-producing photosynthesis. But it might be enough for other types of photosynthesis. One study in 2017 suggested that life on Proxima Centauri b could be about 20% as productive as life on Earth.
Looking for Proxima Centauri b
As of 2026, scientists have not taken a direct picture of Proxima Centauri b. It is too close to its star to be seen clearly. It is also unlikely to pass in front of its star from Earth's view.
Scientists are listening for radio signals from the Proxima Centauri system. The Breakthrough Listen project detected a signal called BLC1 in 2019. However, later studies showed it was likely from human technology.
Future powerful telescopes, like the James Webb Space Telescope and the Nancy Grace Roman Space Telescope, might be able to see Proxima Centauri b directly. It would still be hard to separate the planet's light from its star's light. Scientists hope to observe signs like light reflecting from an ocean or patterns from atmospheric gases.
Even the fastest spacecraft we have built would take about 75,000 years to reach Proxima Centauri. Scientists are working on new technologies for interstellar travel. One idea is to use solar sails that could travel at 20% the speed of light. The Breakthrough Starshot project aims to send tiny probes to Proxima Centauri in the 21st century.
What the Sky Looks Like from Proxima Centauri b
If you stood on Proxima Centauri b, the binary stars Alpha Centauri A and B would look very bright. They would be much brighter than Venus appears from Earth.
Our Sun would look like a bright star in the constellation of Cassiopeia. It would be about as bright as the stars Achernar or Procyon look from Earth.
Images for kids
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Looking towards the sky around Orion from Alpha Centauri with Sirius near Betelgeuse, Procyon in Gemini, and the Sun between Perseus and Cassiopeia generated by Celestia
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This image shows the sizes of the three stars in the Alpha Centauri system compared to other stars, the Sun, and Jupiter.
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This chart shows the constellation Centaurus. The red circle marks the location of Proxima Centauri, the closest star to our Solar System.
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This picture combines a view of the southern skies with images of Proxima Centauri and Alpha Centauri AB from the Hubble Space Telescope.
See also
- Alpha Centauri Bb – a planet once thought to orbit Alpha Centauri B, but later found not to exist.
- Alpha Centauri Ab - a possible planet that might orbit Alpha Centauri A.
- Astrobiology – the study of life in the universe.
- Extremely large telescope – very big telescopes used to study distant objects.
- Exoplanet orbital and physical parameters – details about how exoplanets move and what they are like.
- List of potentially habitable exoplanets – a list of planets that might be able to support life.
 | Aurelia Browder |
 | Nannie Helen Burroughs |
 | Michelle Alexander |
