Gliese 581 facts for kids

Gliese 581 is a small, cool red dwarf star that is not too far from Earth. It's about 22 light years away from our Solar System. This makes it one of the closest stars to the Sun that we know about. You might also hear it called HO Librae, GL 581, or GJ 581.

Scientists called Astronomers have found several planets that orbit Gliese 581. Most astronomers agree that four of these planets are real. However, some scientists believe there might be two more planets orbiting this star.

Gliese 581 is much smaller than our Sun. It has about one-third the radius and mass of the Sun. Its temperature is around 3,498 Kelvin (which is about 4,125 Celsius or 7,457 Fahrenheit). It's also not as bright as the Sun, shining with only about 0.012 times the Sun's luminosity.

You can find Gliese 581 in the sky within the constellation Libra. The star's apparent magnitude is 10.57. This means it's too dim to see with just your naked eye. You would need a telescope to spot Gliese 581.

Planets Around Gliese 581

In 2005, scientists found the first planet orbiting Gliese 581. A team of scientists, led by Stephen Vogt, used a method called Doppler spectroscopy to find this planet. This method helps them learn about a planet's size and other facts. They named this planet Gliese 581b.

Scientists found that Gliese 581b is similar in size to Neptune, the eighth planet in our solar system. It weighs about 16.6 times as much as Earth. Gliese 581b takes only 5.366 days to complete one orbit around Gliese 581.

After this discovery, more scientists started looking for other planets around Gliese 581. In 2007, another group of astronomers announced they had found two more planets. These were named Gliese 581c and Gliese 581d.

For Gliese 581c, scientists measured its mass to be about 5.06 times Earth's mass. This planet orbits Gliese 581 in 12.931 days. For Gliese 581d, they found its mass to be about 8.3 times Earth's mass. Its orbit around the star takes 83.4 days.

In 2009, the first group of astronomers found a fourth planet, which they named Gliese 581e. They measured its mass to be 1.94 times the mass of Earth. This planet has a very short orbit, lasting only 3.149 days. The astronomers also looked at Gliese 581d again. They made more accurate measurements for it. They found Gliese 581d's mass is 7.09 times Earth's mass. Its orbit now seemed to take 66.8 days.

Are There More Planets?

Vogt's group of astronomers later said they found two more planets orbiting Gliese 581. They named these Gliese 581f and Gliese 581g. They shared their findings in 2010. For Gliese 581f, they found a mass of 7.0 Earth masses. Its orbit takes 433 days. For Gliese 581g, they measured a mass of 3.1 times Earth's mass. This planet's orbit lasts 36.6 days.

After Vogt's group announced these new planets, some other astronomers disagreed. In 2012, these other scientists said that planets Gliese 581f and Gliese 581g might not actually exist. Their report suggested that the new findings were false positives. They re-examined the original data and found no clear signs of the two new planets.

However, Vogt's group published even more research to support their claims. Later in 2012, they studied new data from Doppler spectroscopy experiments. They found stronger signs that Gliese 581f and Gliese 581g exist. They also used models to simulate the two different orbit systems. Vogt's group found that a system with only four planets would be unstable. This means it would have broken apart a long time ago. On the other hand, they said that a system with six planets was much more stable.

Today, scientists still don't fully agree on whether planets Gliese 581f or Gliese 581g truly exist.

How Planets Orbit Gliese 581

Scientists are currently looking at two main orbit models for the Gliese 581 system. An orbit model is like a scientific model or hypothesis. It helps astronomers guess how a star's planets move in their orbits. One model suggests four planets with eccentric (oval-shaped) orbits. The other model suggests six planets with circular orbits.

In the first model, some scientists believe that only four planets orbit Gliese 581. These are Gliese 581b, Gliese 581c, Gliese 581d, and Gliese 581e. In this model, none of the planets orbit in a perfect circle. Instead, their paths around the star are ellipses, which are like stretched-out circles.

In the second model, all six planets, from Gliese 581b through Gliese 581g, orbit Gliese 581. In this idea, each planet has a circular orbit around the star.

Comet Belt Around Gliese 581

In November 2012, scientists at the European Space Agency announced an exciting discovery. They found a belt of comets orbiting around Gliese 581. Our own solar system has a similar comet belt called the Kuiper belt.

Could Life Exist on Gliese 581 Planets?

Astronomers believe that Gliese 581 has a "habitable zone". This is the area around a star where it's not too hot and not too cold for liquid water to exist. Liquid water is important for life as we know it on Earth. For Gliese 581, this zone is from about 0.05 AU to 0.24 AU away from the star.

If the six-planet model is correct, then at least two of the planets might be able to support life. This means humans might be able to live there someday. In this model, planet Gliese 581d orbits at the outer edge of the habitable zone. Planet Gliese 581g orbits right in the middle of this zone.

If Gliese 581g has an atmosphere like Earth's, its temperature could be between 236 and 261 Kelvin. This is about -37 to -12 Celsius, or -35 to 10 Fahrenheit. These temperatures are only a little lower than Earth's.

Even if these planets are the right temperature, other things could make them difficult places to live. Planet Gliese 581g might be "tidally locked." This means one side of the planet always faces the star, just like one side of our Moon always faces Earth. If this is true, the side facing the star would be extremely hot. The side always facing away would be extremely cold. Both would be hard for life. Planet Gliese 581d might also be tidally locked.

• Articles about Gliese 581. Space.com articles about Gliese 581

See also

In Spanish: Gliese 581 para niños