Exoplanet

Our Sun is orbited by a lovely array of planets and they are widely diverse- big, small, airless, rocky, gaseous, hot, cold, and more. That makes us think that may be forming planets is easy with so many varieties to choose from.

Even if making planets is hard, there are so many stars in the sky that it’s hard to believe our sun is the only one. Astronomers have fretted over this for a long time, but trying to find such planets is hard.

The biggest problem is any such planets would be faint, far away from being able to see one in a telescope would be like trying to spot a firefly sitting next to a searchlight.

Imagine two kids, one big and one small, facing each other. They clasp hands and start to spin around. As they do, the little kid, who weigh less, will make a big circle, and the bigger kid will make a small circle. The same would be true of a star and planet.

As the planets orbit the star, it makes a big circle or ellipse. But the planets have gravity and it tugs on the star. That means the star makes a small circle and astronomer calls it Reflexive motion.

In 1992, Astronomer Alexander Wolszezan and Dale Frail made and the announcement that they found not just one planet, but 2 orbiting a pulsar (The dead remnant of a star that had exploded).

When a star explodes, its catastrophic event that should destabilize any orbiting planets.

The first true Alien planets had been found officially, which we called Exoplanets.

Pulsar looked like those planets may have formed around the pulsar after the supernova explosion, from the material left over from the catastrophe.

In 1995, Michel Mayor and Didier Queloz found a planet orbiting the star Peg-51, star very much like the sun just 50 light years away.

As the host star of the exoplanets makes its little circle, Sometimes its head towards us and sometimes away that means its light undergo Doppler shift, and that can be detected, It’s not a big shift but it take some equipment to measure it and the planets they found is called 51 Peg b.

For one thing, the orbital period turns out to be just a little over 4.23 days that means the planet is really close to the parent star, just 8 million kilometers out. Compare that to Mercury, which is an average of 55 million kilometer from the sun.

The amount of Doppler shift in the star is related to the mass of the planet; a more massive planet pulls harder on the star, making it move more quickly.

They found the planet was at least half of the mass of Jupiter, and probably more.

But According to planetary formation models, that wasn’t possible. We can’t form a planet that big close to a star, and it turns out the models are probably right. The planet didn’t form close. It probably formed farther out, just like Jupiter. And like Jupiter, it then moved, migrated inward toward the star as it interacted with the disk of a planet-forming material around the star.

In our solar system, Jupiter didn’t get very far in its inward motion- it’s thought that interactions with Saturn’s put the brakes on that, and pulled Jupiter out to where it is now.

Apparently, 51-Peg-B didn’t have its version of Saturn pulling it.  Its spiral continued until it ran out of disk material to interact with which was very close indeed to the star and those planets were called Hot stars

Once 51 Peg B was found, other teams began looking for short period planets, and within a few years several more had been found, many of them hot Jupiter just like 51 Peg-b.

In 1997, A planet called HD-209458b had been discovered on a very short orbit around its star, taking just 3.5days.

From Earth, we see the planets orbit edge on that means once per orbit it directly in front of its star. This event is called a Transit, and when the planet transits the star it blocks a little bit of the star’s light, and that means we can detect it a dip in the star’s brightness.

HD-209458b was the first independent confirmation of an exoplanet, and pretty much everyone was on the bandwagon after that.

The beauty of transiting exoplanet is that the amount of starlight blocked tells us how big the planet is, a big planet blocks more light.

If we know the planet mass from the star’s Doppler shift, we can use the planet’s size to calculate its density.

A gas giant like Jupiter has low density, and a rocky metallic planet like Earth has high density without even being able to see the planets directly we can already start to determine its physically.