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/