Interstellar objects and exoplanet hunting.

“Interstellar object ʻOumuamua sped up as it approached the Sun, shooting past at 196,000 mph (315,431 km/h) and then slowing down as it moved away” (Astronomy, Why aren’t free-floating planets captured when they fly past stars?)

Stars could capture a rogue planet. But that is not as common as many people think. When a planet enters another solar system, it must release its kinetic energy. And rogue planets have a massive amount of kinetic energy. If. That object arrives in the solar system too steeply. its fate would be the star in the middle of the solar system. If. The angle is too shallow. That exoplanet travels straight through the solar system. 

The star could capture a rogue planet if it has the right angle and the right speed. This means that the star should travel behind the planet, following its trajectory. The gravitational brake will slow the planet’s speed. And if that planet arrives in the solar system at the precise right angle. It can start to orbit that star. Things. Like 3/Atlas and other interstellar asteroids. They follow the same rules as larger rogue planets. 

"NASA’s Nancy Grace Roman Space Telescope has successfully powered up its 300-megapixel Wide Field Instrument, a massive infrared camera built to scan huge areas of the sky while preserving Hubble-like detail. Credit: NASA’s Goddard Space Flight Center" (ScitechDaily, NASA’s Roman Telescope Opens Its 300-Megapixel Eye on the Universe)

In reality, we can see only large exoplanets. That. Orbit M-type red dwarfs. 

When we ask whether aliens can see Earth. If. They have similar technology. To. That we have. We can rephrase that question. Can we see an Earth-type planet that orbits its star in the habitable zone? The answer is that a G-spectral-class star is so bright. Its shine. It covers an Earth-type planet. Under its brightness. In planet hunting. Astronomers use methods that benefit from the planet's transit. When. A planet comes between Earth and its own sun. That. Affects the star’s brightness. 

If. The star is small enough. The large exoplanet can affect its trajectory. The wobbling trajectory caused suspicions that Barnard’s Star had exoplanets. Most exoplanets that we know are large. They orbit dim and light stars. And we cannot see Earth-like planets that orbit. Bright stars. The case is similar to Betelgeuse. The brightness of the center star. It covers. The. Dimmer companion under it. Betelgeuse is one of the most well-known stars in the sky. The B-type companion star was confirmed in 31.72026. 

Before astronomers can confirm the existence of the exoplanet. They. Must rule out other possibilities, like changes in the star’s own brightness. Another method astronomers can use is looking for holes in planetary nebulae around stars. Large exoplanets form holes in that nebula. But those nebulae surround only young stars. That method is not suitable for long-distance observations. Things like IR telescopes could see planets through dust and ice. The big problem is that stars also warm dust. 

The surface area of the interplanetary nebula is larger than a planet. And the IR telescopes see that dust. But that dust covers the planet under its IR glow. We can get direct images only from the closest exoplanets. And that requires that they orbit a red dwarf. The reason.  For why. We can see Planets like Proxima B. It is that. They orbit red dwarfs. Those dim stars are dim enough that sensors can measure changes in their brightness. The fact is that. We can’t see a planet that orbits Alpha Centauri or a brighter star. When. A star shines through the exoplanet's atmosphere. That. Allows astronomers. to. make a spectral analysis of the planet’s atmosphere and its chemical fingerprint. This works only with dim stars. That don’t outshine those exoplanets with their brightness. 

https://www.astronomy.com/science/could-aliens-detect-earth-with-our-current-planet-hunting-techniques/

https://www.astronomy.com/science/why-arent-free-floating-planets-captured-when-they-fly-past-stars/

https://www.eso.org/public/news/eso2611/

https://scitechdaily.com/i-jumped-from-my-chair-astronomers-discover-a-hidden-star-orbiting-betelgeuse/

Researchers found the second Earth-size planet in the habitable zone of the TOI 700 system.

"Newly discovered Earth-size planet TOI 700 e orbits within the habitable zone of its star in this illustration. Its Earth-size sibling, TOI 700 d, can be seen in the distance. Credit: NASA/JPL-Caltech/Robert Hurt" (ScitechDaily.com/NASA Planet Hunter Discovers Second Habitable, Earth-Size World in TOI 700 System)

The light exoplanet must be at a longer distance from its star, than the heavy exoplanet that liquid water can exist on its surface. The weak gravitation decreases boiling temperature. And that means the distance to the central star must be longer in the case of weak gravitation planets than in strong gravitation planets. 

If we think that liquid water is the only requirement for life, we must realize that a weak gravitational field decreases the boiling temperature. That means a light exoplanet's habitable zone is at a longer distance from its central star, than a heavy exoplanet. 

So lightweight exoplanet that is quite far away from its star can host life. And heavy exoplanet must be closer to its star so that liquid water can exist on its surface. 

TOI 700 is a red dwarf star in the Dorado constellation, about 101,4 light-years from Earth. The remarkable thing is that the red dwarf has two Earth-size exoplanets in the habitable zone. And that thing causes re-estimation about the descriptions of planets. The TOI 700 system is an extremely compact-size system. 

The TOI 700's surface temperature is about 3000-3500 celsius. And its habitable zone is much thinner than the Sun's habitable zone. So two Earth-size exoplanets in the habitable zone mean those exoplanets are orbiting their star almost by the same trajectory. This is one of the most interesting details about the TOI 700 system.  

We believed that two planets cannot orbit their star by following the same trajectory. But the TOI 700 has shown that two planets might be almost at the same orbiter. That means that also bigger stars can have similar exoplanets. 

The gravitation, not the planet's size, determines if there is liquid water. 

When we search for exoplanets and especially habitable exoplanets. We are facing one thing. There are lots of larger rocky planets than Earth. But some of those exoplanets are lighter than Earth even if they are over 2 times bigger than Earth. 

There are no heavy elements in those exoplanets' mantle or core. And that means their gravitational field is weaker than Earth's. Even their size is bigger. And that is one of the most interesting details in searching for life. 

A weak gravitational field decreases the gas pressure and boiling temperature. 

The exoplanet GJ 436b is a heavy exoplanet. Its gravitation pulls water to ice on its surface. So that thing gives the nickname "world of burning ice for GJ 436b  But there could be an opposite case about the GJ 436b. 

The opposite case could be the lightweight exoplanet that orbits quite far away from its sun. A long-distance allows water could be liquid even if the gravitation is weak. On light exoplanets, the boiling temperature is lower than on heavy exoplanets. 

So if we think only the liquid water the habitable zone of lightweight exoplanets is at a longer distance than heavy exoplanets' habitable zone. And that thing makes this a very interesting thing. 

https://futurism.com/the-strangest-exoplanet-ever

https://scitechdaily.com/nasa-planet-hunter-discovers-second-habitable-earth-size-world-in-toi-700-system/

https://en.wikipedia.org/wiki/TOI_700

https://astronomyandtechnology.blogspot.com/