# Is the Alpha Centauri star system moving closer to us?

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The closest star system after our sun is Alpha Centauri, a three star system with Proxima Centauri, a red dwarf, slightly closer to us than the other 2, around 4.3 light years. I tried Wikipedia and other articles that describe Alpha Centauri and there is plenty of information, but no where could a find an answer to said question.

My presumption is that if the distance is measurable, so should the variance in this distance.

Yes, it's moving closer.

Per Wikipedia.

Source.

In about 30,000 years Alpha Centauri will be 3 (and change) light years away, then it will start moving further away.

If anyone wants to provide a more detailed explanation on stellar movement and charts, please feel free.

Yes the Alpha Centauri system is moving closer and it's not the only one. Barnard's Star, the fastest moving star in our skies, will get close sooner. The major concern is whether or not they will get close enough to disrupt our Oort cloud.

This diagram shows the relative distance of various nearby stars over time. So Alpha Centauri was close to 6LY away 20,000 years ago and will be at its closest position at around 3LY about 30,000 years from now.

## Calculating the journey to Alpha Centauri, our closest star.

I am attempting to calculate the exact time it would take, not counting the necessary slow down upon approach, in order to travel to our closest star system, Alpha Centauri. I want to travel at 11 miles per second, the current speed of Voyager 1.

This is not a homework question. My name is Kyle and I am the creator of the new Trekspertise series over on youtube. This is technically for an upcoming episode.

If Alpha Centauri is 4.37 light years away, traveling at 11 miles per second (346,896,000 miles per year), I calculate it would take 74054.2 years to reach Alpha Centauri.

Is 4.37 light years 25,689,044,200,000.000 miles?

How wrong am I? Any help would be appreciated. Perhaps any help would be credited in the episode?

That's only correct if you assume Alpha Centauri isn't moving. It's actually moving at about 20 miles per second, so the true answer will be different. In fact it's possible your spaceship (at 11 miles per second) would never reach it. You would need to calculate the vector and intercept time for your spaceship given your speed and Alpha Centauri's velocity.

However, without working it out I estimate that your ship will never reach it, but could reach it in about 56,000 years if you go just a little faster: 13.5 miles/second. Alpha Centauri is currently moving closer to us with a radial velocity of 15.6 miles per second, and will reach its closest point in about 28,000 years. So 56,000 years from now it will be at the same distance it is now moving away at 15.6 miles/second, and 74,000 years from now a little farther and moving away a little faster. So your ship, 74,000 years from now, would not quite have reached it and would be not moving fast enough to catch up. At 13.5 miles per second, your ship will reach Alpha Centauri's current distance in 56,000 years, the same amount of time it will take Alpha Centauri to again be at that distance.

If you wanted to intercept it at its closest point to the Sun, youɽ need to go about 22 miles per second and youɽ reach Alpha Centauri in 28,000 years.

## Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2011 July 3
Alpha Centauri: The Closest Star System
Image Credit: 1-Meter Schmidt Telescope, ESO

Explanation: The closest star system to the Sun is the Alpha Centauri system. Of the three stars in the system, the dimmest -- called Proxima Centauri -- is actually the nearest star. The bright stars Alpha Centauri A and B form a close binary as they are separated by only 23 times the Earth- Sun distance - slightly greater than the distance between Uranus and the Sun. In the above picture, the brightness of the stars overwhelm the photograph causing an illusion of great size, even though the stars are really just small points of light. The Alpha Centauri system is not visible in much of the northern hemisphere. Alpha Centauri A, also known as Rigil Kentaurus, is the brightest star in the constellation of Centaurus and is the fourth brightest star in the night sky. Sirius is the brightest even thought it is more than twice as far away. By an exciting coincidence, Alpha Centauri A is the same type of star as our Sun, causing many to speculate that it might contain planets that harbor life.

## Alpha Centauri – the brightest star in the southern Centaurus constellation

Alpha Centauri is the brightest star in the southern Centaurus constellation. It is the closest star system and closest planetary system to Earth’s Solar System at 4.37 light-years (1.34 parsecs) from the Sun. It is the fourth brightest star in the night sky, with a magnitude of -0.01. It is visible in the Southern Hemisphere and is too far south for most of the Northern Hemisphere to see. It could be one of the closest habitable planet prospects to date, although it’s probably not much like Earth if it exists.

Alpha Centauri is the third brightest star in our night sky – a famous southern star – and the nearest star system to our sun. Through a small telescope, the single star we see as Alpha Centauri resolves into a double star.

Alpha Centauri is a binary star system of two stars A & B. There are Alpha Centauri A and B, which are sun-like stars that form a tight binary orbit around one another about 4.37 light-years away. The distance between them is quite close. To the naked eye, the stars are too close for the eye to be able to see them as separate. And then there’s Proxima Centauri, a small red dwarf that’s actually closer to us (4.24 light-years away) and has a much looser gravitational relationship with the other two stars. Their orbit is about the distance of the giant planets from our Sun.

It is a triple star system, consisting of three stars: α Centauri A (officially Rigil Kentaurus), α Centauri B (officially Toliman), and α Centauri C (officially Proxima Centauri). There is a third star, Proxima Centauri (or Alpha Centauri C). Proxima Centauri is orbited by two planets, one of which (Proxima b) seems to be an Earth-size exoplanet in the habitable zone (the region of a star’s orbit where liquid water can form on the surface). This is usually considered separately, but in fact, it is also gravitationally connected to the other two. But Proxima b is thought to be tidally locked and inundated by stellar winds, which means it’s unlikely to be habitable. It is actually slightly closer to us, with a very much larger orbit around A and B.

Viewed as a triple star system, Alpha Centauri is the closest to our own, being 4.2-4.4 light-years (ly) away. The Alpha Centauri system’s potential to host life-bearing worlds has always intrigued scientists, but no known exoplanets have ever been established there—in part because the close proximity meant it was too bright for astronomers to really narrow in on any planetary objects in the area.

Alpha Centauri is a triple star system, with its two main stars, Alpha Centauri A and Alpha Centauri B, being a binary component. It consists of two main stars, Alpha Centauri A and Alpha Centauri B (which form a binary star together) at a distance of 4.36 ly, and a dimmer red dwarf named Proxima Centauri at a distance of 4.22 ly. To the naked eye, Alpha Centauri AB appears to be a single star, the brightest in the southern constellation of Centaurus. Both of the two main stars are rather similar to the Sun. Alpha Centauri A and B are gravitationally bound together, orbiting about a common center of mass every 79.9 years at relatively close proximity, between 40 to 47 astronomical units (that is, 40 to 47 times the distance between the Earth and our sun). The larger star, Alpha Centauri A, is the most similar to the Sun, but a little larger and brighter.

## On alpha Centauri

2015 (October 12, to be exact) marks the hundredth anniversary of the discovery of Proxima Centauri by the Scottish astronomer Robert Thorburn Ayton Innes, the director of the Union Observatory in Johannesburg, South Africa. Proxima was quickly recognized to be the smallest member of the alpha Centauri star system, and is now known to be the closest star to the Solar System. (The closest star to Earth is, and remains, the Sun… as various professors were apt to remind me over the years).

The alpha Centauri star system, famed of song, story, and videogames, is the closest star system to us (again, apart from the one we’re currently in). It’s 4.3 light years away, or 1.3 parsecs, or about 270,000 times farther from the Earth than the Sun is (AU)… which is still depressingly far away for anyone who would want to visit it with currently achievable tech: it’s taken New Horizons 9 years to travel 35 AU so it would take about 69,000 years to get to Proxima Centauri at that speed (71,000 years to alpha Centauri A and B). alpha Centauri A has a spectral type of G2V, which means it’s a star very much like the Sun (it is, in fact, slightly more massive and slightly hotter). alpha Centauri B has a spectral type of K1V, which means it’s a few hundred degrees cooler and has a mass about 80% of the Sun. A and B are about the same distance apart as Uranus is from the Sun, and they orbit every roughly 80 years. Proxima Centauri (or alpha Centauri C) is an M5.5Ve star, which means it’s about 16% of the mass of the Sun, two thousand degrees Kelvin cooler than the Sun, and sits 15,000 AU (15,o00 times the distance from Earth to the Sun) from A and B. Its orbital period is… unknown, but if it’s circular and the total system mass is 2 solar masses, Proxima’s orbit is something like 1.3 million years long. Proxima Centauri is so far from A and B that every so often astronomers, armed with new data, reconsider whether it’s actually gravitationally bound to the pair. (The answer always turns out to be “yes”) The alpha Centauri system is probably around 6 billion years old, and it’s so close to us that Proxima Centauri is a little over 2 degrees from A and B on the sky, or the width of four full moons. There are no planets in the system, though for a while it was thought that there was an Earth-mass planet in a 3.2 day orbit (so, a ball of molten lava) of alpha Centauri B. The alpha Centauri system is very, very well studied.

The alpha Centauri system was first suspected of being nearby because of their high proper motion, or apparent motion across the sky. Being stars, we’re not talking night-to-night movement like the ancients saw with the planets. Rather, this is motion best understood over a period of years, because the orbit of the star system around the Galaxy is slightly different from our own. In the case of alpha Centauri, they’re all so close to us that they appear to move (relatively) quickly through space. Seriously, here’s ten years of motion of Proxima Centauri (2000-2010):

The proper motion of Proxima Centauri (Rigil Kentaurus C) as seen on CTIOPI astrometric images from 2000-2010

An asteroid in the asteroid belt can move that far in the space of a few minutes, but Proxima moves pretty fast for a star.

And that brings us to a much more recent paper: A discovery of a new object near alpha Centauri. This hasn’t been getting all that much press, but plenty of astronomers have been talking about it on Twitter. Basically, what this group of ALMA researchers have found is a source near alpha Centauri A and B that seems to be moving very fast they suggest the object is alpha Centauri D.

There are many problems with this, which is why the paper ended up on the preprint server in the first place: A discovery this remarkable begs for an explanation, and at the time they posted it, the ALMA people had none.

First off: how was this not seen before? In ALMA’s favor, alpha Centauri is so incredibly bright (A is the third brightest star in the sky B would be 21st on its own) that it’s hard to see anything close to them. But if this was a star that bright compared to A and B, it should be pretty bright itself (an M2 star, which would be brighter and MORE massive than Proxima Centauri), and shouldn’t have escaped the notice of absolutely everyone until now.

Second: this alpha Centauri D object appears (Figure 1 in the paper on page 2) to have moved significantly compared to alpha Cen A and B. In 2014, it was hovering between the two stars, and then in 2015, it was directly above alpha Cen A. That could be orbital motion, except that it’s a LOT of orbital motion for one year. A and B orbit each other every 80 years, and they barely seem to move between the two images. This mystery object is farther away than B, which means its orbital period should be even longer, and it shouldn’t have moved AT ALL. They basically admit in their own table 1 (columns 2 and 3) that the motion of this object is nothing like the known members of alpha Centauri.

That suggests that this alpha Cen D is actually something else entirely. If its motion isn’t the same as alpha Centauri, a few years (or decades, or a century ago) it should have been far enough from alpha Centauri that it could have been EASY to spot on its own. Innes should have seen it back in 1915.

So maybe it’s not a star. Maybe it’s a closer object in the outer reaches of our own solar system. In that case, it’s moving awfully slowly. There’s actually a second paper from ALMA that found ANOTHER source moving at 87 arcseconds per year (ten times faster than the fastest star, so more plausibly a member of the Solar System) that the discoverers think would have to be a distant planet in our Solar System. Then again, noted Solar System astronomer Mike Brown (@plutokiller on twitter) did the math and figured out that if ALMA found a planet in the outer Solar System after such a short search, statistically there ought to be 200,000 Earth-sized planets in the outer solar system, which is absurd.

So… what IS it? Or, what are these?

There are a couple likely possibilities. It could be a detector flaw that nobody has noticed before it could be the equivalent of a cosmic ray making a bright spot appear where there really isn’t anything. It’s probably two different sources ALMA usually can’t see, where one flared up in 2014 and one in 2015… two separate stars (or two distant quasars) that appeared out of nowhere because they finally became bright enough to be seen… This sort of thing actually happens all the time. Take a look at the .gif of Proxima Centauri above and you can see a few sources that are only visible in one or two of the frames due to the different exposure times and sky brightness. A string of mistaken identities could become measurements of a moving star. The reverse is also true occasionally a high proper motion star (particularly a really high proper motion one like Proxima Centauri) will wander into a field of view and be mistaken for a new object.

There are other options astronomers are exploring, and that’s really the purpose of all of this. Science is allowed to be wrong, but put enough minds together and it’s self-correcting. For now, though, Proxima Centauri remains the closest star to Earth, and alpha Centauri the closest star system.

## The Closest Star System To Ours Doesn't Have Any Planets (Yet), After All

Image credit: ESO/L. Calçada/Nick Risinger (skysurvey.org).

If you had looked to the skies just 25 years ago, you'd only be able to wonder about planets around other stars. "They must be there," you'd reason, "since there's no way our Solar System is unique in all the galaxy." But where's the proof? As the case always is in science, it's in the data you collect and in the measurements and observations you make.

Over the past generation, we've not only successfully found thousands of planets by multiple different methods, but we've been able to measure:

• their mass (by the pull on their parent star),
• their radius (by the amount of light that they block),

Our limitations are that our current techniques were only really useful for measuring certain kinds of planets.

The planets that are closer in mass to their parent star pull more strongly, and so are easier to measure. Get a Sun-like star with an Earth-like planet, and we wouldn't be able to see it.

The planets that are closer in physical size to their parent star and that are aligned with our line-of-sight to the star block a larger fraction of its light, enabling us to see it better. Again, an Earth-like planet around a Sun-like star would be barely visible and right at the limit of what the Kepler mission could've found.

And the planets that are closer in to their parent star -- closer even than Mercury is to the Sun -- are easier to detect, since they provide us with more "cycles" to observe than the more distant, slowly moving worlds.

In 2012, scientist Xavier Dumusque and his collaborators announced something spectacular: the closest star system to the Sun, the Alpha Centauri trinary system (consisting of the Sun-like Alpha Centauri A, its lower-mass binary companion Alpha Centauri B, and the tiny, very distant trinary member, Proxima Centauri), had a planet around one of its stars! Alpha Centauri B, it appeared, had a planet orbiting very close to it, completing an orbit around the star every 3.24 days! (For comparison, Mercury takes 88 days to orbit the Sun.)

Image credit: PHL @ UPR Arecibo, via . [+] http://phl.upr.edu/press-releases/aplanetarysystemaroundourneareststarisemerging.

The way it was measured was through what's known as the radial velocity method, where a planet's gravitational tug on a star causes it to appear to move towards us, then away from us, then towards us again in a periodic, well-defined fashion. This results in a phenomenon known as stellar wobble, and so by measuring the frequency and magnitude of the wobbling, we can determine the mass and orbital properties of the planet that must be there. The "wobble" meant that the star moved back-and-forth by an extra speed of just 0.0005 km/s every 3.24 days. And it was measured over a long enough baseline that other explanations -- internal magnetic properties of the star, instrumental noise, or the tug of other companion stars -- couldn't be the cause. It seemed they had truly discovered a planet.

Image credit: PHL @ UPR Arecibo, via . [+] http://phl.upr.edu/press-releases/aplanetarysystemaroundourneareststarisemerging.

But it wasn't to be so! There isn't a planet there, but the data was telling us a planet was there. The hard truth is this: we tricked ourselves because of how we measured this data. You see, in an ideal world, you'd monitor a star continuously, 24 hours a day, observing its signal constantly. In the real world, you only do it when you have access to the telescope (when it's not being used for other purposes), at night, and when the sky is both clear and has good enough atmospheric conditions to see what you're aiming at.

Image credit: PHL @ UPR Arecibo, via . [+] http://phl.upr.edu/press-releases/aplanetarysystemaroundourneareststarisemerging.

So what you might want to imagine is that you're flying over the surface of the Earth, looking down, and measuring your distance to the ground. But instead of measuring it continuously, you're only measuring it at a few specific points. Are you in a mountain range? Atop a plateau? Hitting the tops of a series of foothills? Or flying over a craggy ice sheet?

Image credit: Vinesh Rajpaul, via http://blog.oup.com/2016/01/ghost-planets-mystery/.

If all you knew was to look for a mountain range, you might reach that conclusion. But that's not necessarily the only, or the correct, explanation. In this particular case -- of looking at Alpha Centauri B and inferring a planet -- the data was consistent with a planet, but a planet not only wasn't the only explanation, it didn't turn out to be the correct explanation.

Image credit: Rajpaul, Aigrain and Roberts, 2015. Via http://arxiv.org/pdf/1510.05598v1.pdf.

By subtracting out the inherent variation in the star itself, the team accidentally amplified other periodic signals, one recurring one of which was mistaken for a planet. That signal turned out to be the rotation of the star itself, which has only now been accounted for properly. Interestingly enough, when all the analysis is done properly, there's a hint of a signal for a different planet significantly farther out: with a period of about 20 days. The innermost planet of Alpha Centauri B turned out to be a false signal, and not actually there at all. But even though the closest star system to us doesn't have the planet we thought it did after all, the game is far from over. The first real planets around this trinary star system may be just right around the corner!

## Planets in Alpha Centauri Star System:

In 2012, Scientist found that there is a planet like Earth in this star system which revolves around the Alpha Centauri B and it is named as Alpha Centauri Bb. Probably, it may be equalize and mass of the Earth. Also, it is believed that it may be a rocky planet like Earth. Moreover, its orbital length may be 6 million km.

Proxima Centauri has two planets which are named as Proxima b and Proxima C. The first one is an earth sized exo-planet that discovered in 2016. The second one is an exo-planet in habitable zone that is discovered in 2019.

## Lingering Problems

Despite being based off established tech, issues are still present. The size of each chip makes it hard to cram all the instruments needed onto it. Sprite, by the Mason Peck group, is the best option with a total mass of 4 grams and minimal effort needed to produce. However, each Starchip needs to be 1 gram and carry 4 cameras as well as sensory equipment. Each of those cameras wouldn’t be like a traditional lens apparatus but a plasma Fourier capture array which implements diffraction techniques to gather wavelength data (Finkbeiner 35).

And how would Starshot send the data back to us? Many satellites use a single watt diode laser but the range is limited to just that of the Earth-Moon system distance, something that is closer to us than Alpha Centauri by a factor of 100 million. If sent from Alpha Centauri, the transmission would degrade to just a few hundred photons, nothing of consequence. But maybe if an array of Starchips were left as specified intervals, they could act like a relay and ensure better transmission. One could expect a kilobit per second as a reasonable transmission rate (Finkbeiner 35, Choi).

Powering that transmitter however is another big issue. How would you power a Starchip for 20 years? Even if you can power a chip with the best tech around, only a minimal signal would be sent. Maybe minute pieces of nuclear material could be an extra source, or perhaps friction from travelling in the interstellar void could be converted into wattage (Finkbeiner 35).

But that medium could also bring death to Starchips. So many unknown dangers exist in it that could take it out. Maybe if the chips were coated with beryllium copper it could provide extra protection. Also, by increasing the number of chips launched, the more can be lost and still ensure mission survives (Ibid).

But what about the sail component? It needs a high level of reflectivity to ensure that the laser powering it simply doesn’t melt it away as well as to propel the chip to the speed needed. The reflectivity part can be solved if gold or solver are used, but lighter materials would be desired. And, crazy as it sounds, refractive properties would be needed too because the chip would be going so fast that red-shifting of the photons would ensue. To ensure the chip and sail can make it at the requisite velocity, it needs to be from 1 atom to 100 atoms (about 1 soap bubble) in thickness. Ironically, the hydrogen and helium that the chips may encounter on their journey would pass through this sail with no damage to it. And the max damage dust will likely entail is just 0.1% of the entire sail&aposs surface area. Current tech can get us a sail that is 2,000 atoms thick and can get the craft going at 13 g’s. For Starshot, 60,000 g would be needed to get the chip to the desired 60,000 kilometers per second (Finkbeiner 35, Timmer).

And of course, how could I forget the laser which will set this whole operation into motion? It would need to be 100 gigawatts in power which we can achieve already, but only for a billionth of a trillionth of a second. For Starshot, we need the laser to last for minutes. So use an array of lasers to get to the 100 gigawatt requirement. Easy, right? Sure, if you can get 100 million of them in a 1 square kilometer area and even if that was achieved the laser output would have to contend with atmospheric disturbances and the 60,000 kilometers between the laser and the sail. Adaptive optics could help and are a proven tech but never on the scale of millions. Problems, problems, problems. Also placing the array high in a mountainous area will reduce atmospheric disturbances, therefore the array would likely be built in the Southern Hemisphere (Finkbeiner 35, Andersen).

## Is there life in the Alpha Centauri system?

The search for life on other planets is fascinating, challenging, and enlightening. If successful, it will teach us about ourselves, where we come from, and what our destiny is. Scientists from the University of Hawaii, including Jeff Kuhn, David Harrington, and John Messersmith, are part of a team headed by Prof. Dr. Svetlana Berdyugina (Kiepenheuer Institut fuer Sonnenphysik and the University of Freiburg, Germany, and a visiting scientist at the University of Hawaii NASA Astrobiology Institute) that has developed a new approach to searching for life on other planets. Biologist Tina &Scaronantl-Temkiv of Aarhus University, Denmark, is also a team member.

### Photosynthetic biopigments

The team has measured various biological photosynthetic pigments in the laboratory. They absorb almost all solar light of specific colors in the visible and convert it into chemical bonds to store energy. For example, chlorophyll pigments absorb blue to red light and reflect a small part of green in the visible, as seen in green plants. (Figure 1).

All infrared light is reflected, and this is employed in agriculture to monitor water content in crops. Such biopigments are contained in plants, algae, bacteria, and even in human skin (carotenoids) and eyes (rhodopsin), creating the colored beauty of our world. They can also help find life on the surfaces of other planets.

Figure 1: A green leaf absorbs almost all red, green and blue light (RGB), but it reflects and transmits infrared light (shown in grey). The reflected infrared light is only weakly polarized due to the reflection of a healthy leaf, but the reflected RGB light is strongly polarized due to biopigments. Measuring the amount of polarized light at different colors reveals the signature of the leaf biopigments. Green sand reflects and polarizes sunlight almost equally in all wavelengths, which distinguishes it from a leaf that is a similar color. Similarly, yellow plants are different from yellow sand, etc. (Credit: S. Berdyugina)

The scientists have found that the part of visible light reflected by various plants with vibrant colors oscillates in certain directions, while incident light oscillates in all directions (Figure 1). Thanks to this peculiarity, this reflected light can be detected remotely by using polarizing filters (similar to Polaroid sunglasses or 3D movie goggles) when viewed at specific angles even if the star is millions of times brighter than the planet. The team found that each biopigment has its own colored footprint in such polarized light.

Modeled spectra reflected off distant exo-Earth surfaces have demonstrated the advantage of using polarized light to distinguish photosynthetic biosignatures from minerals, ocean water and the atmosphere. The high contrast of the biosignatures in the polarized light is the key to finding them in the overwhelmingly bright stellar light that usually hides the exoplanetary signals.

These results will be published by the International Journal of Astrobiology, Cambridge University Press [1]. Earlier Prof. Berdyugina and her team employed polarized light to see for the first time the blue color of an exoplanet [2]. Now this method can help to see colors of life on other planets, even at large distances from the sun.

### Our neighbor, the triple stellar system Alpha Centauri

This technique could be instrumental in searching for life in the planetary system nearest to the sun, Alpha Centauri, with existing telescopes. There are three stars in this system. While scientists are interested in finding life around all these stars, Alpha Centauri B, only 4.37 light years from Earth, seems optimal for life searches with current telescopes (Figure 2).

Figure 2: The Alpha Centauri A and B stars with their habitable zones (green ovals) as seen projected on the sky. The habitable zones appear as an ovals because the planets' orbits are inclined to our line of sight. For the same reason, the distance between the A and B stars appears shortened. If there are planets in the habitable zones (blue dots), photosynthetic biopigments could be detected with the proposed polarimetric technique. Sizes of the stars and planets are not to scale. (1 AU = the distance between Earth and the sun.) (Credit: S. Berdyugina)

In 2014, a small planet was discovered around Alpha Centauri B. Unfortunately, this exoplanet is ten times closer to the star than Mercury is to the sun, so its surface is melting under the stellar heat, and it probably has no atmosphere. At a distance where planets like Earth with liquid water on their surface could exist (the &ldquohabitable zone&rdquo), no planets have been found as yet, but scientists are continuing to search for one. If such a planet is found, or even before that, it is possible to search for photosynthetic biosignatures in the Alpha Centauri B spectrum. Using the proposed polarization technique, this task becomes even more feasible.

Figure 3: Artist&rsquos impressions of Earth-like planets covered by photosynthetic organisms with terrestrial-like biopigments studied by the team. (Credit: S. Berdyugina & C. Giebink).

This research was supported at KIS/Freiburg by the European Research Council (ERC) Advanced Grant HotMol (http://hotmol.eu), the Leibniz Association (WGL) grant InnoPol, and the UH NASA Astrobiology Institute team.

### References:

[1] Berdyugina, S.V., Kuhn, J.R., Harrington, D.M., &Scaronantl-Temkiv, T., Messersmith, E.J.: Remote Sensing of Life: Polarimetric Signatures of Photosynthetic Pigments as Sensitive Biomarkers, International Journal of Astrobiology, in press (2015)

Founded in 1967, the Institute for Astronomy at the University of Hawaii at Manoa conducts research into galaxies, cosmology, stars, planets, and the sun. Its faculty and staff are also involved in astronomy education, deep space missions, and in the development and management of the observatories on Haleakala and Maunakea. The Institute operates facilities on the islands of Oahu, Maui, and Hawaii.

## The closest star system found in a century

A pair of newly discovered stars is the third-closest star system to the Sun and the closest discovered since 1916. At 6.5 light years, it is so close that Earth's television transmissions from 2006 are now arriving there. It is an excellent hunting ground for planets because it is very close to Earth and, in the distant future, it might be one of the first destinations for manned expeditions outside our solar system. The discovery was made by Kevin Luhman, an associate professor of astronomy and astrophysics at Penn State University and a researcher in Penn State's Center for Exoplanets and Habitable Worlds. In this image, the star system, WISE J104915.57-531906, is at the center of the larger image, which was taken by the WISE satellite. It appeared to be a single object -- but a sharper image from the Gemini Observatory revealed that it is a binary star system. Credit: NASA/JPL/Gemini Observatory/AURA/NSF

(Phys.org) —A pair of newly discovered stars is the third-closest star system to the Sun, according to a paper that will be published in Astrophysical Journal Letters. The duo is the closest star system discovered since 1916. The discovery was made by Kevin Luhman, an associate professor of astronomy and astrophysics at Penn State University and a researcher in Penn State's Center for Exoplanets and Habitable Worlds.

Both stars in the new binary system are "brown dwarfs," which are stars that are too small in mass to ever become hot enough to ignite hydrogen fusion. As a result, they are very cool and dim, resembling a giant planet like Jupiter more than a bright star like the Sun.

"The distance to this brown dwarf pair is 6.5 light years—so close that Earth's television transmissions from 2006 are now arriving there," Luhman said. "It will be an excellent hunting ground for planets because it is very close to Earth, which makes it a lot easier to see any planets orbiting either of the brown dwarfs." Since it is the third-closest star system, in the distant future it might be one of the first destinations for manned expeditions outside our solar system, Luhman said.

The star system is named "WISE J104915.57-531906" because it was discovered in a map of the entire sky obtained by the NASA-funded Wide-field Infrared Survey Explorer (WISE) satellite. It is only slightly farther away than the second-closest star, Barnard's star, which was discovered 6.0 light years from the Sun in 1916. The closest star system consists of Alpha Centauri, found to be a neighbor of the Sun in 1839 at 4.4 light years, and the fainter Proxima Centauri, discovered in 1917 at 4.2 light years.

A pair of newly discovered stars is the third-closest star system to the Sun and the closest discovered since 1916. At 6.5 light years, it is so close that Earth's television transmissions from 2006 are now arriving there. It is an excellent hunting ground for planets because it is very close to Earth and, in the distant future, it might be one of the first destinations for manned expeditions outside our solar system. The discovery was made by Kevin Luhman, an associate professor of astronomy and astrophysics at Penn State University and a researcher in Penn State's Center for Exoplanets and Habitable Worlds. This diagram illustrates the locations of the star systems that are closest to the Sun. The year when each star was discovered to be a neighbor of the Sun is indicated. The binary system WISE J104915.57-531906 is the third nearest system to the Sun, and the closest one found in a century. Credit: Janella Williams, Penn State University

Edward (Ned) Wright, the principal investigator for the WISE satellite, said "One major goal when proposing WISE was to find the closest stars to the Sun. WISE 1049-5319 is by far the closest star found to date using the WISE data, and the close-up views of this binary system we can get with big telescopes like Gemini and the future James Webb Space Telescope will tell us a lot about the low mass stars known as brown dwarfs." Wright is the David Saxon Presidential Chair in Physics and a professor of physics and astronomy at UCLA.

Astronomers have long speculated about the possible presence of a distant, dim object orbiting the Sun, which is sometimes called Nemesis. However, Luhman has concluded, "we can rule out that the new brown dwarf system is such an object because it is moving across the sky much too fast to be in orbit around the Sun."

To discover the new star system, Luhman studied the images of the sky that the WISE satellite had obtained during a 13-month period ending in 2011. During its mission, WISE observed each point in the sky 2 to 3 times. "In these time-lapse images, I was able to tell that this system was moving very quickly across the sky—which was a big clue that it was probably very close to our solar system," Luhman said.

After noticing its rapid motion in the WISE images, Luhman went hunting for detections of the suspected nearby star in older sky surveys. He found that it indeed was detected in images spanning from 1978 to 1999 from the Digitized Sky Survey, the Two Micron All-Sky Survey, and the Deep Near Infrared Survey of the Southern Sky. "Based on how this star system was moving in the images from the WISE survey, I was able to extrapolate back in time to predict where it should have been located in the older surveys and, sure enough, it was there," Luhman said.

A pair of newly discovered stars is the third-closest star system to the Sun and the closest discovered since 1916. At 6.5 light years, it is so close that Earth's television transmissions from 2006 are now arriving there. It is an excellent hunting ground for planets because it is very close to Earth and, in the distant future, it might be one of the first destinations for manned expeditions outside our solar system. The discovery was made by Kevin Luhman, an associate professor of astronomy and astrophysics at Penn State University and a researcher in Penn State's Center for Exoplanets and Habitable Worlds. This image is an artist's conception of the binary system WISE J104915.57-531906 with the Sun in the background. Credit: Janella Williams, Penn State University

By combining the detections of the star system from the various surveys, Luhman was able to measure its distance via parallax, which is the apparent shift of a star in the sky due to the Earth's orbit around the Sun. He then used the Gemini South telescope on Cerro Pachón in Chile to obtain a spectrum of it, which demonstrated that it had a very cool temperature, and hence was a brown dwarf. "As an unexpected bonus, the sharp images from Gemini also revealed that the object actually was not just one but a pair of brown dwarfs orbiting each other," Luhman said.

"It was a lot of detective work," Luhman said. "There are billions of infrared points of light across the sky, and the mystery is which one—if any of them—could be a star that is very close to our solar system."