Thousands of exoplanets are already known – now the task is to identify particularly exciting specimens. This is exactly what astronomers have now achieved once again: They have discovered a “hot super-earth” in our cosmic neighborhood, which is ideally suited to “look through” and analyze its atmosphere with the telescopes that will soon be available. This would allow atmospheric models of rocky planets to be checked. This in turn is of great importance for assessing the characteristics of distant worlds and their friendliness, say the researchers.
In the last two and a half decades, planet hunters have found many distant celestial bodies into the net and they have also been able to uncover basic features of some: By combining different observation techniques, masses, sizes and thus densities can be identified, which in turn enables conclusions to be drawn about the composition of the exoplanets. Now the curious gaze of astronomers is increasingly turning to the atmospheres of the distant worlds – the earth-like rock planets are particularly in their sights. Because in the case of our homeland, the gas envelope made life possible. Insights into the characteristics of the gas envelopes could enable spectral analyzes of the light that shimmers through the atmospheres of the exoplanets as they pass in front of their central star. The characteristics of the light can then provide information about the presence of certain substances in the atmosphere.
Distant gas envelopes in sight
Insights into the atmospheres of distant rocky planets, however, represent a comparatively great challenge. If they exist at all, they only consist of a thin layer that is difficult to analyze. In this context, however, astronomers have high hopes for the performance of the next-generation telescopes and observatories. But even for their “keen eyes”, exoplanets must meet certain requirements so that informative insights into their atmospheres can be achieved.
Against this background, the researchers led by Trifon Trifonov from the Max Planck Institute for Astronomy in Heidelberg are now presenting the planet Gliese 486b. An important aspect of this celestial body is that it orbits a dwarf star that is only 26 light years away from us. “The proximity of this exoplanet is exciting because we can examine it more closely with powerful telescopes such as the James Webb Space Telescope and the future Extremely Large Telescopes,” explains Trifonov. And that could be worthwhile, as the team’s research results so far show. Methods of transit photometry and radial velocity spectroscopy were used – based on data from various telescopes.
Close and promising
Gliese 486b is therefore a so-called super-earth with 2.8 times the mass of the earth and 30 percent larger in extent. If you stood on Gliese 486b, you would be exposed to an attraction that is 70 percent stronger than on our home planet, the scientists make clear. As they explain, the planet’s mean density indicates that it is a rocky planet with a similar composition to Venus and Earth – including a metallic core.
Compared to these planets in our solar system, however, Gliese 486b orbits its parent star extremely closely: at a distance of only 2.5 million kilometers within 1.5 days. Gliese 486b always faces the same side of the star, because its rotation around its own axis takes just as long as the orbit, according to the results. Although the dwarf star Gliese 486 is much fainter and cooler than the sun, its close proximity means it heats the planet to at least 430 degrees Celsius.
Its surface is therefore probably shaped by a landscape that is criss-crossed by glowing lava flows. For the investigation of the atmosphere, however, these conditions are apparently favorable: “The discovery of Gliese 486b was a stroke of luck. A hundred degrees hotter and the entire surface of the planet would be lava. As a result, its atmosphere would consist of evaporated rock, ”says co-author José A. Caballero from the Centro de Astrobiología in Madrid. “If Gliese 486b, on the other hand, were a hundred degrees colder, this would also be unfavorable for subsequent observations.”
Perspective planned
The scientists plan to examine the promising celestial body using the method of transit spectroscopy. It becomes possible when Gliese 486b moves over the surface of its central star from our perspective. A tiny fraction of the starlight shines through the presumably thin atmosphere before it reaches Earth. The various compounds it contains absorb light at certain wavelengths and thus leave a characteristic signature in the light. With the help of spectrographs, astronomers can then split the light into wavelengths and look for the absorption characteristics that provide clues about the composition of the atmosphere.
The team is also planning studies using emission spectroscopy, which could allow conclusions to be drawn about the features of the planet’s surface. It can be used when parts of the illuminated hemisphere, such as phases of the moon, become visible during Gliese 486b’s orbit until it disappears behind the star. The spectrum can then provide information about the bright, hot planetary surface, so the hope. “We can hardly wait until the new telescopes are available,” says Trifonov. “The results will help us to understand how well rocky planets can hold their atmospheres, what they are made of and how they influence the distribution of energy on the planet,” says the scientist.
Source: Max Planck Institute for Astronomy, specialist article: Science, doi: 10.1126 / science.abd7645
Video: Virtual flight to the planet Gliese 486b. (Credit: RenderArea)