Our planet's oceans produce light signatures when sunlight reflects off them. The same may be done by planets with ocean coverage. Can we use the Earth's reflectance signatures to identify other Earth-like worlds with large oceans?
Eventually, we should be able to.
A new study looked at light signatures reflecting off of Earth's oceans. Two Earths, one dry and one wet, were modeled by the researchers. They did a simulation of how light would reflect from those planets. The ocean can cause the light to dip in certain ways.
The journal Astronomy and Astrophysics will publish the study, but it is currently available online. V.J.H. Trees and D.M. Stam are the authors. Stam and Trees are both from the Royal Netherlands Meteorological Institute.
When the planet is in front of its star and the starlight passes through the atmosphere, scientists have found water on exoplanets. There is no way of knowing if there is an ocean because the observations revealed the water's signature.
Estimates show that up to one-quarter of known exoplanets have oceans. Earth is the only planet with surface oceans. Some of the dwarf planets in the Solar System have oceans.
As telescope technology improves, we may be able to detect oceans on planets similar to Earth. Habitability signatures can be found with future telescopes if the simulations of starlight reflected by Earth-like exoplanets are correct.
There are three things that the researchers computed in their exoplanet simulations. They modeled the oceans in a particular way. The reflected light is in the same plane as the incident light. Augustin-Jean Fresnel is the name of parallel polarization. He invented a lens that focused light into a narrower beam.
The starlight isn't expected to be polarization so it's important to measure it. Light signals degrade with distance, but the degree of polarization doesn't. Current ground-based and space-based telescopes can't measure the ocean-reflected light that is reflected by Earth-like exoplanets.
That will change.
The upcoming European Extremely Large Telescope (E-ELT), and the Large Ultraviolet Optical Infrared Surveyor (LUVOIR), a space telescope concept being developed by NASA, will both be able to measure light. The instruments and observation procedures needed to sense the polarization of light reflected by exo-oceans will be designed using numerical models.
The degree of Ps is one of the main findings from this work. The image compares the Ps for cloud-free dry planets and cloud-free ocean planets.
The main lesson is that Ps only dips in certain circumstances. As the authors point out, dips in Ps are only observed for ocean planets and only when the glint is cloud-free.
It will be a landmark event if we discover an exoplanet with an ocean. The space science community is pretty confident that they can support life. When scientists measure an exoplanet's density vs its size, there are hints of exo-oceans. There is no way of knowing if we are detecting a surface ocean.
The problem of detecting exo-oceans has been worked on by these researchers for a while now. We may be able to detect ocean worlds at great distances if their simulations are correct. The E-ELT will be able to detect starlight reflected from the ocean.
Maybe we will have our first confirmed ocean exoplanet soon after.
More:
All Rights Reserved © 2024
