portten.blogg.se - Tidal locking

On the other side of the planet, these season are reversed. Sun is getting closer and you can feel it. Sun is getting closer, but also further below the horizon. Sun falls back to the horizon and shrinks some more. Sun rises a few degrees off the horizon and also shrinks. This is due to the planet moving at different speeds while rotating at a fixed speed.įor people living in the twilight zone will see the sun rise and set over the year and this will be much more important than the distance to the sun. If you have a tidally locked planet in an eccentric orbit, the tidal lock isn't perfect. This is correct.īut there is one important aspect of this situation neither answer mention.

The variable distance from the sun makes the planet hot or cold. During the (shorter) time that it's near the star, it's summer.īoth the other answers (at this time) suggests making the orbit eccentric. During the time that it is farther from its star, it will be winter on the entire planet. What if the planet has a different type of orbit? Imagine your planet has an orbit like the one shown below. A planet in a circular orbit with no tilt will not have seasons. OK, so if you have a planet like the Earth with a (roughly) circular orbit and the same part of that planet is always facing its star and there's no tilt, then you would not have seasons. The varying amounts of sunlight around the Earth

Sometimes the Sun is in the direction that the Earth is pointing, but "pointing" to one side as it goes around the Sun. We have seasons because the earth is tilted (wonky) as it makes its Let's start with an overview of why there are seasons. I'm drawing on my answer to a different question here. Even if you're not satisfied with the orbital eccentricity approach, there are other options. Indeed, these seasons will remain long after the orbit has circularized.Įssentially, you have some room to play around. For instance, I've argued that if its parent star is a variable star, it can experience seasonal variations comparable to the ones we've discussed based only on orbital eccentricity. Now, our planet can get seasons though other mechanisms. Therefore, winter will be longer than summer. Winter comes because the planet is further from the star, but Kepler's second law tells us that planets further away move slower.

The seasons will be different lengths.

Seasons due to axial tilt affect each hemisphere in opposite ways in our case, the entire planet is moving closer and further from the star.

The changes due to the seasons will be more uniform, globally.

This has a couple of notable consequences: Why? Well, the temperature variations are now entirely due to the orbit, rather than the tilt of the rotation axis. Now, seasons on this planet would be a little bit different from seasons on Earth. That's a difference of 46 Kelvin - certainly enough to cause some variation in climate. Putting this together, we see that the planet should reach a temperature of 1706 Kelvin at its closest point, and a temperature of 1662 Kelvin at it farthest point. Therefore, its closest approach to the star is $0.0467$ AU, and its farthest point is $0.0492$ AU. It orbits at a distance of $a=0.0481$ AU. However, its orbit isn't perfectly circular - in fact, it has an eccentricity of $e=0.023\pm0.015$ (almost twice that of Earth's!). Let's do some calculations with an exoplanet known to be tidally locked.Īstronomers believe that the planet Tau Boötis b is tidally locked to its parent star. However, planets in closer to their stars tidally lock quicker, meaning that a planet close to its star could have a non-negligible seasonal variation while still being tidally locked. Tidal locking requires long timescales, and over those same timescales, tidal forces from the star will work to circularize the orbit, reducing its eccentricity and therefore the magnitude of these seasonal differences. The change in the energy received is likely to be small. This will be the case for any orbit with a non-zero eccentricity. This means that over the course of a single orbit, this planet would receive different amounts of light from the star as it slowly moves away and then towards it. Just like normal planets, tidally-locked planets don't need to have perfectly circular orbits. Seasons can definitely occur on a tidally locked planet.