First Earth-Sized Planet in Habitable Zone

The last few decades have been an exciting time for the exploration of other solar systems. So many exoplanets have been found, with the total going from literally zero to thousands. First with Kepler, then Spitzer, and now TESS — the Transiting Exoplanet Survey Satellite — which can detect minute fluctuations in the light emitted by target stars as their planets transit in front of their suns. This has been described as analogous to analysing the light from a lit-up skyscraper at night and being able to detect someone shifting down their office blind by one centimetre! More on TESS here.

All the planets of interest identified by the TESS will be classified with the TOI prefix ( Transiting Exoplanet Survey Satellite Object of Interest).

TESS has already had its first find. An Earth-sized planet in the habitable zone of the star designated TOI 700, which is 100 lightyears away. Cosmic spitting distance! For the astronomically minded, this star is in the constellation of Dorado. It’s so exciting  to imagine these stars as fostering a solar system favourable to life. TOI 700 is a cool M dwarf star, also known as a red dwarf star, the coolest in the cosmic stellar sequence, the most common, and the longest-lived stars. This red dwarf has 50% of our Sun’s surface temperature, and 40% of its radius — like a cool little sister.

TOI700 d First Earth-Sized Planet in a Habitable Zone

The planet that all the excitement is about is TOI 700 d, which is the outermost of three identified planets in that system. It is estimated to be around 20% larger than Earth, with an orbital period of 37 days, receiving perhaps 86% of the energy that our Sun provides to Earth. All three planets in this system are thought to be tidally locked to their star. This means they rotate once per orbit, with one face always toward its sun and the other permanently facing away — day and night sides — much like how the Moon is tidally locked to Earth.

Based on our solar system, we are used to the idea of rocky planets existing closer to the sun, with gas giants appearing further out. In TOI 700 the closest planet to the sun (TOI 700 b) is Earth-sized and rocky, the second (TOI 700 c) is likely have a composition similar to Neptune, while the goldilocks third planet (TOI 700 d) is Earth-sized and rocky!

What makes TOI 700 d unique is that it’s the first Earth-sized exoplanet located in the habitable zone. Astronomers have found thousands of Jupiter-sized planets, many of them “hot Jupiters” that orbit very close to their star, and other rocky planets, some of which are Earth-sized, but all of which lay outside the zone where liquid water might exist on their surface.

The only hitch for TOI 700 d is that despite receiving less solar energy, it is thought to be receiving up to 35 times more extreme UV radiation, which is not so great news for developing life. Regardless, TOI 700 d is a solid candidate for a habitable world, and one in our close stellar neighbourhood.

Future work will be targeted at characterisation of the planets’ atmospheres, and if possible, their actual compositions. Given the fact that they are likely to be tidally locked, the 3D climate modellers are going to have their work cut out for them!

The likelihood that the three planets in this system might be tidally locked has really tickled my SF brain, since one of the major premises of my SF book The Tau Ceti Diversion, was that the target planet (where all the action takes place) is tidally locked to its sun.

The Tau Ceti Diversion . . . with the crew dead, and the starship’s fusion drive held back from a lethal explosion, Karic and the surviving officers finally reach a habitable planet. The last thing they expected was to find it already occupied . . .

Get The Tau Ceti Diversion here!

The twin Earth almost had

It’s hard to imagine Mars as a wet place, but that’s exactly what the data and images coming in from the Curiosity rover in Gale Crater are telling us. In fact, Mars is the twin Earth almost had.

Wet Mars.

3.5 billion years ago Gale Crater was filled with ponds of water, with streams cascading down the ancient basin’s walls, down to its wet centre. Eventually these watercourses dried up, but then perhaps the whole cycle repeated numerous times. Of course the water did eventually go for good.

Why?

Unlike Earth, which has a powerful magnetic field protecting its atmosphere, Mars has no such advantage. The solar wind — all those energised particles — just ram straight into it, knocking molecules right out of its atmosphere into space. Which molecules go first? The lightest ones. The hydrogen, the water, the oxygen. What is left is the heavier molecules like carbon dioxide, purely by virtue of the balance between gravitational attraction and the applied force of that solar wind. But that’s planet formation!

How do scientists conclude that there may have been these super wet and dry periods from the geology? By evidence left in the rocks, specifically high concentrations of mineral salts, deposited during periods of evaporation. This is not the first time Curiosity has found evidence of water here. The rover has also unearthed evidence of freshwater lakes.

Gale Crater: Source NASA JPL

The Gale crater itself started life with a bang, and is thought to have been formed by one massive impact. Sediment on the floor of the crater was built in layer upon layer of alluvial deposits, drying into a substantial formation over time. This layered rock was later wind-eroded to form the current Mount Sharp, which Curiosity is busily climbing.

So, we know there was water there, and likely there for long periods of time. The 64 million dollar question is, was this wet environment capable of supporting microbial life at the surface, and if so, for how long? How long were evolution’s engines allowed to turn, working to transform that life? And is that life still present?

If not for the weak magnetic field of Mars, we could have had a celestial twin. A planet in our own solar system with water-based life. Now that is something to think about!

Studies like this are invaluable in understanding our own home. As a SF writer, they provide invaluable insights when it comes to building your own planets! Check out my own world-building in The Tau Ceti Diversion.

With the crew dead, and the starship’s fusion drive held back from a lethal explosion, Karic and the surviving officers reach a habitable planet – the last thing they expected was to find it already occupied . . .

Get it now on Amazon!