Exoplanet, 356 light years from Earth

NASA has released James Webb Webb Space Telescope's photo of exoplanet HIP 65426b, the first direct image of an exoplanet taken by the Webb Telescope, 356 light-years from Earth.

Exoplanets are usually not luminous and cannot be directly observed with telescopes, and it is difficult to spot them.

What is so special about HIP 65426b, the first exoplanet photographed by the Webb telescope, and is it suitable for human habitation?

The universe is vast and empty, and the distance between stars is often tens or hundreds of light years. At such a distance, most stars will become dim, and only some stars with large masses can be seen with the naked eye.

But on the one hand, we want to discover extraterrestrial civilizations, and on the other hand, we want to find a second home for human beings, so exoplanet observation is the way to the sea of stars.

The most common method to determine the presence of planets near stars is the sunset method.

When a planet passes around a star, it blocks part of the star's light, making the starless bright. After a period of continuous observation, if the change in brightness is regular and periodic, it means that there is probably a planet orbiting the star, but sometimes the star is so bright that even if there is a planet over the sun, it will still be submerged in the star's halo, and then an interference space satellite is needed to remove the star's powerful halo and discover the planet.

Although simple and commonly used, the sunset method has some limitations: it can only see planets of stars that are in the same plane as the Earth.

When the libation method is not applicable, it is also possible to determine the presence of planets by the faint displacement of the star. In our solar system, the gravitational pull of the Sun pulls the eight planets and makes them revolve around it periodically, and if the planet is massive enough, its gravitational pull also affects the Sun, making it exist in a very small orbit around the planet.

When two celestial bodies revolve around each other, the spectrum emitted by the star will show a Doppler shift, relying on this principle scientists can determine whether there are planets around the star by observing the faint displacement of the star over time.

These two methods may seem troublesome, but they are also the easiest and most direct ways to find exoplanets. Since the discovery is so difficult, how does the Webb telescope directly image HIP 65426b?

Webb telescope is not the first human observation of HIP 65426b, as early as 2017, the European Observatory Very Large Telescope in Chile first discovered HIP 65426b, but in trying to understand it further, the infrared light emitted by the planet was blocked by the Earth's atmosphere, thus unable to obtain more details about it.

In contrast, the Webb telescope is located on the backside of the second Lagrangian sunspot, where the Sun's light is blocked by the Earth, and the Webb telescope can be unaffected by the Sun. More importantly, the Webb telescope is equipped with the extremely sensitive Mid-Infrared Explorer (MIRI), the workhorse of Webb imaging, which operates at a temperature of less than 7 Kelvin (-226°C).

At this temperature, the effect of its infrared light on observations can be greatly reduced. Because the light from distant galaxies is so faint, if the instrument is kept at its normal temperature, then its infrared light will obscure the light of the observed object, just as it is difficult to spot a firefly under a searchlight.

In addition, this photo is also thanks to the corona graph Webb carries, as we mentioned above, the strong light from the star will mask the light from the exoplanet, for example, HIP 65426b's parent star is 10,000 times stronger than it, and it is almost impossible to observe it directly under normal circumstances.

But on the one hand, the distance between HIP 65426b and its parent star is 100 times the Earth-sun distance, which helped scientists to identify it in the image, and on the other hand, it is because the corona graph obscures the distant star, reducing the strong light interference.

With all this effort, what are the specifics of the planet?

In this photo, the white pentagram is the parent star HIP 65426, which is obscured by the coronagraph, and the yellow-orange spot is HIP 65426b, which is 356 light-years away, orbiting about 100 times farther from its parent star than the Earth is from the Sun, which makes it take a full 630 years to revolve around its parent star.

While we live on a planet that is 4.5 billion years old, HIP 65426b is only 14 million years old, making it a very young planet that has extreme heat and brightness because the planet has not yet cooled and the heat from its formation is still exerting its residual heat.

Scientists estimate that the surface temperature of HIP 65426b is at least 900 degrees Celsius, while the temperature of Mercury, the closest planet to the Sun in our solar system, is only 427 degrees Celsius.

Unlike Earth, HIP 65426b is a gaseous planet, similar to Jupiter, and although its surface features are not visible in the images, scientists believe it may look like Jupiter with cloud bands caused by changes in temperature and composition, and spots in its atmosphere caused by storms or cortices.

In this way, it is clear that HIP 65426b is not suitable for any life, but this is not the main point of the Webb telescope to observe it, with the first directly imaged exoplanet, there will be more later, and the Webb telescope's road to the stars is just beginning.