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NASA discovers an Earth-size planet in a star’s ‘habitable zone’

NASA’s specialised planet-hunting spacecraft searching for signs of alien life has spotted an Earth-sized world within its star’s habitable zone.

Dubbed TOI 700 d, the planet is just 100 light years away and is slightly larger than Earth.

It has a much swifter orbit than Earth, taking just 37 days to complete a trip around its star. 

TOI 700 d also receives just 86 per cent of the energy Earth does, due to its star being around 40 per cent the mass of our Sun and only half as hot.   

Its presence within the habitable zone and its size offers hope that it may host liquid water, but this has not yet been confirmed.  

The breakthrough from the TESS spacecraft was announced during the annual American Astronomical Society meeting in Honolulu, Hawaii.

 

Dubbed TOI 700 d, the planet is just 100 light years away, exceptionally close on the scale of space. It is slightly larger than Earth and has a much swifter orbit time of just 37 days

TESS found three planets around the star, with only one inside the habitable zone, where the temperature would allow for liquid water to exist on its surface.  

‘TESS was designed and launched specifically to find Earth-sized planets orbiting nearby stars,’ said Paul Hertz, NASA astrophysics division director.

The exoplanet – a world orbiting a star that is now our Sun – was almost missed by astronomers after an initial error wrongly categorised the star and its planets.

Scientists wrote the planets off as non-viable for extraterrestrial life as they were thought to be too big and too hot. 

But a team of amateur astronomers, including a high school student, identified the error and corrected it.   

‘When we corrected the star’s parameters, the sizes of its planets dropped, and we realised the outermost one was about the size of Earth and in the habitable zone,’ said Emily Gilbert, a graduate student at the University of Chicago.

The discovery was later confirmed by the Spitzer Space Telescope.  

Similar planets have been identified before, including some spotted by the now defunct Kepler Space Telescope.

But this marks the first such world spotted by TESS after its 2018 launch. 

TESS spots distant planets with a patient approach, it studies the image of stars in a specific region of the night sky and waits for objects to pass in front of it. 

These transits often indicate the presence of an orbiting planet making its way around the star and the drop in the star’s luminosity is analysed to provide clues to the world’s size, speed and chemical composition of its atmosphere.   

TESS found three planets around the star, with only one inside the habitable zone, where the temperature would allow for liquid water to exist on its surface. Pictured, one simulation allowing for liquid water on the planet#s surface which shows TOI 700d in the habitable zone

TESS found three planets around the star, with only one inside the habitable zone, where the temperature would allow for liquid water to exist on its surface. Pictured, one simulation allowing for liquid water on the planet#s surface which shows TOI 700d in the habitable zone 

WHAT IS TIDAL LOCKING?

Tidal locking is the phenomenon which sees a moon appear fixed in place around a planet, with only one side being visible. 

This happens when the rotational period – time it takes to spin 360° – is the same as the time it takes to complete one orbit. 

The lunar cycle is an example of this, with the moon completing one trip around Earth every 28 days, the same time it takes to spin around entirely.

it is because of tidal locking that the ‘dark side of the moon’ exists.  

But despite the best efforts of the astronomers, the scientists are still unsure what the planet is made of but are conducting computer simulations to try and find out.    

The planet is tidally locked to the star, meaning that one side always faces the star, as is the case with the Moon and Earth.

One simulation included an ocean-covered TOI 700 d with a dense, carbon-dioxide-dominated atmosphere similar to what scientists suspect surrounded Mars when it was young.   

This synchronous rotation meant that, in another model, one side of the planet was constantly covered in clouds.

Another model predicts the planet to be TOI 700 d as a cloudless, all-land version of modern Earth, where winds flow away from the night side of the planet and converge on the point directly facing the star. 

A third simulation predicted an all-land world, where winds flow from the planet’s dark side to its light one.

Multiple astronomers will observe the planet with other instruments, in order to obtain new data that may match one of NASA’s models.

HOW DO SCIENTISTS STUDY THE ATMOSPHERE OF EXOPLANETS?

Distant stars and their orbiting planets often have conditions unlike anything we see in our atmosphere. 

To understand these new world’s, and what they are made of, scientists need to be able to detect what their atmospheres consist of.  

They often do this by using a telescope similar to Nasa’s Hubble Telescope.

These enormous satellites scan the sky and lock on to exoplanets that Nasa think may be of interest. 

Here, the sensors on board perform different forms of analysis. 

One of the most important and useful is called absorption spectroscopy. 

This form of analysis measures the light that is coming out of a planet’s atmosphere. 

Every gas absorbs a slightly different wavelength of light, and when this happens a black line appears on a complete spectrum. 

These lines correspond to a very specific molecule, which indicates it’s presence on the planet. 

They are often called Fraunhofer lines after the German astronomer and physicist that first discovered them in 1814.

By combining all the different wavelengths of lights, scientists can determine all the chemicals that make up the atmosphere of a planet. 

The key is that what is missing, provides the clues to find out what is present.  

It is vitally important that this is done by space telescopes, as the atmosphere of Earth would then interfere. 

Absorption from chemicals in our atmosphere would skew the sample, which is why it is important to study the light before it has had chance to reach Earth. 

This is often used to look for helium, sodium and even oxygen in alien atmospheres.  

This diagram shows how light passing from a star and through the atmosphere of an exoplanet produces Fraunhofer lines indicating the presence of key compounds such as sodium or helium 

This diagram shows how light passing from a star and through the atmosphere of an exoplanet produces Fraunhofer lines indicating the presence of key compounds such as sodium or helium 

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