Tau Ceti – One of Our Celestial Neighbours

The Tau Ceti system is indeed one of our close cosmic neighbours. At less than 12 lightyears away, it is one of the closest systems to Earth’s own solar system – along with others such as the Centauri system and Epsilon Eridani. Because of its nearness to our own solar system, it has been a favourite in science fiction for decades. A likely first or second step for any intrepid interstellar explorers.

I first started toying with the idea of a novel set in the Tau Ceti system more than twenty years ago. And as these things go, the story developed in fits and starts as I bounced between novel projects and other stories. One of the things about writing science fiction, particularly near-future SF, is that the science never stands still. And particularly, in the last few decades, the developments in astronomy and the identification of planets outside our solar system, called exoplanets, has been almost exponential!

When I wrote the first draft of The Tau Ceti Diversion, there was not a single confirmed planet identified outside Earth’s solar system. Now, thanks largely to the latest Kepler space-based telescope discoveries, there are more than 3000! Not only that, but there have been five identified in the Tau Ceti system itself, with one – and possibly two – in the habitable zone around that star.

What did this mean for me? It meant a ton of research, and lot of very careful rewriting!

In my very early drafts of The Tau Ceti Diversion, I was free to imagine an Earth-like solar system of planets and shape them as I saw fit for the story. But by the time the last draft was completed, only months ago, I had very specific information about what those planets might be. I knew their approximate mass, their orbits, even their eccentricity. I had to go back to the drawing board – and my excel spreadsheets – to try and work out how these known planets would fit within the very specific constraints of my story. Not the least of which was that my story included a tidally locked planet!

It’s no accident that the Tau Ceti system has been popular as a setting for science fiction. Even before the identification of its family of planets, Tau Ceti, in the constellation of Cetus, was known to be very similar to our own Sun. It is smaller, about 78% of the Sun’s mass, and is the closest solitary G-class star (the same spectral class as the Sun). That’s enough to make it seem like our cousin. Add to that Tau Ceti’s stability, and lack of stellar variation, and you already feel like moving in. The only hitch is the presence of a debris disk, which means that any planet orbiting Tau Ceti is likely to face more impact events than planets in our own solar system.

Seen from Tau Ceti, the Sun would appear much like Tau Ceti does to us – a third magnitude star visible to the naked eye.

The composition of Tau Ceti, as measured by the ratio of its iron to hydrogen content, or metallicity, is lower than our Sun, indicating that it is older: its makeup derived from earlier stars yet to manufacture the same amount of heavy elements in their internal fusion factories.

So similar to our own Sun, and so close, it’s no wonder that it is also a target for the SETI (Search for Extra-Terrestrial Intelligence) program.

As readers of my novel The Tau Ceti Diversion will discover, the explorers in my novel certainly find some intelligent life there!

Read it now on Amazon!

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Our Closest Earth-like Planet

In an amazing stroke of cosmic luck, our closest Earth-like planet Proxima b turns out to be orbiting our closest star, Proxima Centauri, only 4.2 lightyears away!

The Kepler space telescope has been expanding our knowledge of exoplanets – planets outside the solar system – for years now. The number of confirmed exoplanets from Kepler now exceeds 3000, and the rate at which our knowledge of these planets is increasing is truly amazing. Kepler is able to give us data on planets thousand of lightyears from our own little corner of the universe.

So it came as a surprise, a number of months ago, when the very closest potentially Earth-like, habitable planet, turned out to be so close. Unlike its very bright neighbours, Alpha and Beta Centauri, which can easily be seen with the naked eye, you need special equipment just to see Proxima Centauri!

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Photo: space.com

Proxima Centauri is a red dwarf, one of the most common stars in the universe. In a bit of stellar Karma, it turns out that little stars like Proxima have much longer lifetimes that the bigger, brighter white or blue stars, or even our own yellow star, surviving for trillions of years – plenty of time for life to take hold if the conditions are right.

Astronomers have been trying to unlock Proxima Centauri’s secrets for more than 15 years, using two instruments from the European Southern Observatory in Chile – the Ultraviolet and Visual Echelle Spectrograph (UVES) and the High Accuracy Radial velocity Planet Searcher (HARPS). Both instruments focus on deciphering the star’s ‘wobbles’. So why did it take so long? The detection was made more difficult by sparse data, and the long-term variability of the star itself, which masked the presence of the planet. With new, key observations made in 2016, the astronomers were able to confirm not only Proxima b, but also reveal indications of a possible second planet with an orbital period of between 60 and 500 days also orbiting around Proxima Centauri.

Observations indicate Proxima b is around 1.3 times heavier than Earth, putting it into the rocky planet category. Although the planet is in the habitable zone, it orbits at only around 7.5 million kilometres, completing an orbit every 11.2 Earth days. Due to the closeness to its host planet, astronomers consider it likely that the planet is tidally locked, divided into halves of night and day, and always showing the same face to Proxima Centauri. Earth orbits at 150 million kilometres, much further out from our brighter, hotter sun, but still in our habitable zone. The temperature is right on the planet for surface water to exist, but much depends on the planet’s history. If its star was very active, the water may have been blown away in its early formation, whereas if the planet migrated inward at a later stage, it might be water rich.

So Proxima b’s in the habitable zone, which means it may have surface water, but will it have life? On the pessimistic side, it turns out that Proxima Centauri emits powerful flares and X-ray radiation. That may work to erode the atmosphere of the planet, although we don’t know how much because we don’t know if the exoplanet has a nice, strong magnetic field like Earth that would help to preserve the atmosphere and protect any developing life.

We need to go and have a look. But how to get there?

If we could shrink down to about two inches tall, we could hitch a ride on something like NASA’s New Horizon’s probe, which managed its trip to Pluto in around 9.5 years at around 84,000 km/h. That would get us a sneak peek of Proxima b in around 54,400 years. Hmmn. Or maybe the hotshot Juno probe that reached a whopping 265,000 km/h? That would cut the trip to 17,157 years.

One option is to accelerate a small probe with solar sails to relativistic speeds using a high powered laser. Just such a thing has been proposed by the Breakthrough Starshot initiative. For around $18 billion we could build a system that would send wafer-thin probes to Proxima Centauri. The Earth-based laser would accelerate the probes to around 20 percent the speed of light (215.85 million km/h). That would get the tiny probes to Proxima Centauri in 20 to 25 years. What these small probes could tell us will rely very much on how powerful their miniaturized instruments were, and of course scientists being able to conceive a way for a targeted message to reach Earth with the data.

It’s exciting that we have an Earth-like planet so close to our solar system. How we get there is one thing, but if human history tells us anything, once we want to go there – we will find a way.

My novel, The Tau Ceti Diversion, a story about our search for new planets to colonise outside our solar system, and is now available on Amazon! Read more about what happens in the story here!

Check out the free chapter download!

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Hot Young Planets

One of the real mysteries of identified exoplanets is the how many very large planets – the size of our Jupiter and even larger – are so close to their parent stars. This is a strange thing for us Terrans, because in our solar sytem, all our gas giants are in outer orbits. A situation so familiar anything else just seems plain wrong.

hot jupter

These ‘hot jupiters’ – heated by their proximity to their parent stars – are often in very close orbits to their suns, more equivalent to the orbit of say Mercury in our own solar system.

So how did they get there? Did they form there, or did they somehow migrate there? Were they wandering planets that were captured by their new suns?

At first these hot jupiters were considered anomalies, but as the list of exoplanets grew, astronomers found – to their surprise – that these type of planets were common. So what’s up? Is our solar system really the odd one out? It would be interesting if that was true, since the position of our own gas giants was crucial to the formation of higher life forms on Earth. Jupiter acted like a cosmic vacuum cleaner, stopping the multiple asteroid impacts that would have driven life on Earth back to basics time and time again.

The Spitzer telescope has been observing a hot Jupiter called HD 80606b, 190 lightyears from Earth, that has a highly eccentric orbit, swinging around its star every 111 days.

The theory is that these hot jupiters start out in highly eccentric orbits around their stars (like a very flat or ‘skiny’ ellipse), swinging first closer, then further out from their star. Over a period of hundreds of millions of years, gravitational influences from nearby stars or planets drive them into circular orbits, which are close to their parent stars. Part of this process is thought to be the loss of the planet’s gravitational energy as heat as it passes close to its parent star.

In HD 80606b, astronomers think they are observing one of these gas giant exoplanets in the middle of its migration. We still see the highly eccentric orbit, but it is now swinging very close to its parent star, moving toward its final, closer, circular orbit.

I don’t think we have a hundred million years to find out if this theory is correct, but at the rate our exoplanet discoveries are coming in, we will certainly have more data, and perhaps enough snapshots of multiple hot jupiters to get a good idea of exactly what’s happening in solar system formation.

My novel, The Tau Ceti Diversion, a story about our search for new planets to colonise outside our solar system, is due to be launched on September 1st 2016! Read more about what happens in the story here!

Check out the NASA post on HD 80606b, and the cool graphics, here.

 

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Thank You Kepler! Thousands of New Exoplanets Now Confirmed

The number of new confirmed exoplanets – planets located outside our own solar system – continues to grow at an impressive rate.

A massive amount of data is collected by space-based telescopes, which has to then be analysed and verified by astronomers. In the largest single announcement yet, NASA scientists have released information on 1,284 new verified planets, pared down from 4,302 potential candidates. When only decades ago there was not a single verified exoplanet, that number becomes staggering.

kepler - thousands of new planets

This announcement more than doubles the number of confirmed planets identified by the Kepler space telescope. And with every new verified planet identified, the odds of identifying a true Earth-analogue increase.

Before Kepler was launched, astronomers had no idea how common planets really were. Now it is thought that there are likely to be more planets than stars. When you realise there are billions of galaxies, each with millions of stars, that’s a lot of planets! Even if the chance of life was extremely low, the likelihood of life, possibly even intelligent life out there somewhere starts to look good.

Missions like Kepler, combined with new technologies for getting actual pictures, spectrographic analysis and thermal maps of exoplanets (check out this post on capturing planetary snapshots), all point to some very exciting discoveries in the not-so-distant future.

Of the newly identified Kepler planets, around 550 could be Earth-like rocky planets. Nine of these orbit in their sun’s habitable zone, now making a total of 21 confirmed exoplanets in the so-called ‘goldilocks’ zone where liquid water can exit on the planet’s surface, allowing the potential for the formation of life as we know it. Two of these habitable zone planets are in the Tau Ceti system (see here). The potential for life on one of these planets is explored in my novel The Tau Ceti Diversion, due to be launched on September 1st 2016! Read more about what happens in the story here!

Kepler truly is the workhorse of planet-finding. Of the 3.200 exoplanets identified to date, more than 2,325 of these were discovered by Kepler. Launched in March 2009, Kepler spent four years monitoring the same patch of sky – some 150,000 stars – watching for the telltale tip in a star’s brightness that indicates a transiting planet.

Let’s hope that Kepler, and other missions like it, continue to increase our knowledge of exoplanets far into the future.

 

Capturing our First Planetary Snapshots

 

Kepler has confirmed more than 1000 planets outside our solar system, but so far only a few of Earth-like size and in the habitable zone — rocky planets with just the right temperature for liquid water. And none of those potential Earth-analogues have been observed directly, but through the interpretation of astronomical data, such as the wobble of the star, or the dimming on the star’s light due to planetary transit.

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So far, some pictures of other planets have been taken from ground-based telescopes, but those planets are large, bright and orbit far from their suns — not like potential Earth-twins which will be far smaller and orbit closer to their suns.

NASA scientists and engineers are working on two new technologies to help look for new planets, a starshade and a coronagraph, which will both work to block the light of the star, allowing the telescope to examine the reflected light of the planet itself.

This means we can not only take pictures of prospective Earth-like planets, but also use spectrographic analysis to analyse what in their atmospheres as well. This will give us clues to what might exist there. For example, evidence of plant life and animals similar to those on our Earth would show up as a series of simple signature compounds in the planet’s atmosphere: such as oxygen, ozone, water and methane.

A starshade is a type of spacecraft that actually flies in front of the telescope to block the light of the sun under observation. Despite the fact it will be only tens of metres wide, it will fly quite a bit in front of the telescope — in fact around 50,000 km away — more than four Earth diameters. Getting it into space is a challenge. It will be folded up like a super-origami prior to launch to unfurl in space,  somewhat like an unwinding spring, into to a crazy-sized sunflower. The pointed petals are crucial to its design: they control the light the right way to reduce the glare to levels where planets can be seen. The petal-fringed shape creates a softer edge that causes less bending of the light waves.

Both the starshade and the telescope will be independent spaceships, allowing them to move into just the right position for observations. The petals of the starshade need to be positioned with millimetre accuracy.

Blocking out the starlight while preserving the light emitted from the planet is called starlight suppression.

The light of a sun can be billions of times brighter than the reflected light from the planet. Our own sun is 10 billion times bright than Earth.

Coronagraphs were originally introduced in the early 20th century to study our own sun, blocking out the light from the sun’s disk to allow scientists to study its outer atmosphere, or corona; hence coronagraph. They are much smaller than the starshade, located within the telescope itself.

These starlight-blocking coronagraphs will be more sophisticated.

These new generation coronagraphs uses multiple masks as well as smart mirrors that can deform, to suppress starlight in sequential stages. There are many other challenges in delivering the coronagraph technology, including being able to suppress or compensate for the warping and vibrations that all space telescopes experience.