Artist's conception of the Kepler Space Telescope. Credit: NASA/JPL-Caltech
It’s alive! NASA’s Kepler space telescope had to stop planet-hunting during Earth’s northern-hemisphere summer 2013 when a second of its four pointing devices (reaction wheels) failed. But using a new technique that takes advantage of the solar wind, Kepler has found its first exoplanet since the K2 mission was publicly proposed in November 2013.
And despite a loss of pointing precision, Kepler’s find was a smaller planet — a super-Earth! It’s likely a water world or a rocky core shrouded in a thick, Neptune-like atmosphere. Called HIP 116454b, it’s 2.5 times the size of Earth and a whopping 12 times the mass. It circles its dwarf star quickly, every 9.1 days, and is about 180 light-years from Earth.
“Like a phoenix rising from the ashes, Kepler has been reborn and is continuing to make discoveries. Even better, the planet it found is ripe for follow-up studies,” stated lead author Andrew Vanderburg of the Harvard-Smithsonian Center for Astrophysics.
Kepler ferrets out exoplanets from their parent stars while watching for transits — when a world passes across the face of its parent sun. This is easiest to find on huge planets that are orbiting dim stars, such as red dwarfs. The smaller the planet and/or brighter the star, the more difficult it is to view the tiny shadow.
Infographic showing how the Kepler space telescope continued searching for planets despite two busted reaction wheels. Credit: NASA Ames/W Stenzel
The telescope needs at least three reaction wheels to point consistently in space, which it did for four years, gazing at the Cygnus constellation. (And there’s still a lot of data to come from that mission, including the follow-up to a bonanza where Kepler detected hundreds of new exoplanets using a new technique for multiple-planet systems.)
The drawback is Kepler needs to change positions every 83 days since the Sun eventually gets in the telescope’s viewfinder; also, there are losses in precision compared to the original mission. The benefit is it can also observe objects such as supernovae and star clusters.
Kepler-62f, an exoplanet that is about 40% larger than Earth. It’s located about 1,200 light-years from our solar system in the constellation Lyra. Credit: NASA/Ames/JPL-Caltech
“Due to Kepler’s reduced pointing capabilities, extracting useful data requires sophisticated computer analysis,” CFA added in a statement. “Vanderburg and his colleagues developed specialized software to correct for spacecraft movements, achieving about half the photometric precision of the original Kepler mission.”
That said, the first nine-day test with K2 yielded one planetary transit that was confirmed with measurements of the star’s “wobble” as the planet tugged on it, using the HARPS-North spectrograph on the Telescopio Nazionale Galileo in the Canary Islands. A small Canadian satellite called MOST (Microvariability and Oscillations of STars) also found transits, albeit weakly.
A paper based on the research will appear in the Astrophysical Journal.
An artistic image of the explosion of a star leading to a gamma-ray burst. (Source: FUW/Tentaris/Maciej Fro?ow)
Gamma ray bursts (GRBs) are some of the brightest, most dramatic events in the Universe. These cosmic tempests are characterized by a spectacular explosion of photons with energies 1,000,000 times greater than the most energetic light our eyes can detect. Due to their explosive power, long-lasting GRBs are predicted to have catastrophic consequences for life on any nearby planet. But could this type of event occur in our own stellar neighborhood? In a new paper published in Physical Review Letters, two astrophysicists examine the probability of a deadly GRB occurring in galaxies like the Milky Way, potentially shedding light on the risk for organisms on Earth, both now and in our distant past and future.
There are two main kinds of GRBs: short, and long. Short GRBs last less than two seconds and are thought to result from the merger of two compact stars, such as neutron stars or black holes. Conversely, long GRBs last more than two seconds and seem to occur in conjunction with certain kinds of Type I supernovae, specifically those that result when a massive star throws off all of its hydrogen and helium during collapse.
Perhaps unsurprisingly, long GRBs are much more threatening to planetary systems than short GRBs. Since dangerous long GRBs appear to be relatively rare in large, metal-rich galaxies like our own, it has long been thought that planets in the Milky Way would be immune to their fallout. But take into account the inconceivably old age of the Universe, and “relatively rare” no longer seems to cut it.
In fact, according to the authors of the new paper, there is a 90% chance that a GRB powerful enough to destroy Earth’s ozone layer occurred in our stellar neighborhood some time in the last 5 billion years, and a 50% chance that such an event occurred within the last half billion years. These odds indicate a possible trigger for the second worst mass extinction in Earth’s history: the Ordovician Extinction. This great decimation occurred 440-450 million years ago and led to the death of more than 80% of all species.
Today, however, Earth appears to be relatively safe. Galaxies that produce GRBs at a far higher rate than our own, such as the Large Magellanic Cloud, are currently too far from Earth to be any cause for alarm. Additionally, our Solar System’s home address in the sleepy outskirts of the Milky Way places us far away from our own galaxy’s more active, star-forming regions, areas that would be more likely to produce GRBs. Interestingly, the fact that such quiet outer regions exist within spiral galaxies like our own is entirely due to the precise value of the cosmological constant – the factor that describes our Universe’s expansion rate – that we observe. If the Universe had expanded any faster, such galaxies would not exist; any slower, and spirals would be far more compact and thus, far more energetically active.
In a future paper, the authors promise to look into the role long GRBs may play in Fermi’s paradox, the open question of why advanced lifeforms appear to be so rare in our Universe. A preprint of their current work can be accessed on the ArXiv.
Imagine, if you would, a potential future for humanity… Imagine massive space-elevators lifting groups of men, women, and children skyward off Earth’s surface. These passengers are then loaded onto shuttles and ferried to the Moon where interstellar starships are docked, waiting to rocket to the stars. These humans are about to begin the greatest journey humanity has ever embarked upon, as they will be the first interstellar colonists to leave our home Solar System in order to begin populating other worlds around alien stars.
There are many things we must tackle first before we can make this type of science-fiction scene a reality. Obviously much faster methods of travel are needed, as well as some sort of incredible material that can serve to anchor the aforementioned space elevators. These are all scientific and engineering questions that humanity will need to overcome in the face of such a journey into the cosmos.
But there is one particular important feature that we can begin to tackle today: where do we point these starships? Towards which system of exoplanets are we to send our brave colonists?
Of all of the amazing things we need to discover or invent to make this scene a reality, discovering which worlds to aim our ships at is something that is actually being worked on today.
Artistic view of a possible space elevator. Image Credit: NASA
It’s an exciting era in astronomy, as astronomers are currently discovering that many of the stars that we view in the night sky have their own planets in orbit around them. Many of them are massive worlds, all orbiting at varying distances from their parent star. It is no surprise that we are discovering a vast majority of these Jupiter-sized worlds first; larger worlds are much easier to detect than the smaller worlds would be. Imagine a bright spotlight pointing at you some 500 yards away (5 football fields). Your job is to detect something the size of a period on this page that is orbiting around it that emits no light of its own. As you can see, the task would be daunting. But nevertheless, our planet hunters have been utilizing methods that enable us to accurately find these tiny specks of gas and rock despite their rather large and luminous companion suns.
However, it is not the method of finding these planets that this article is about; but rather what we do to figure out which of these worlds are worthy of our limited resources and attention. We very well cannot point those starships in random directions and just hope that they happen across an earth-sized planet that has a nitrogen-oxygen rich atmosphere with drinkable water. We need to identify which planets appear to have these mentioned characteristics before we go launching ourselves into the vast universe.
How can we do this? How is it possible that we are able to say with any level of certainty what a planet’s atmosphere is composed of when this planet is so small and so very far away? Spectroscopy is the answer, and it just might be the key to our future in the cosmos.
Artistic impression of what Kepler-186f may look like. Image Credit: NASA Ames/SETI Institute/JPL-CalTech
Just so I may illustrate how remarkable our scientific methods are for this very field of research, I will first need to show you the distances we are talking about. Let’s take Kepler 186f. This is the first planet we have discovered that is very similar to Earth. It is around 1.1 times larger than Earth and orbits within the habitable zone of its star which is very similar to our own star.
Let’s do the math, to show you just how distant this planet is. Kepler 186f is around 490 lightyears from Earth.
Kepler 186f = 490 lightyears away
Light moves at 186,282 miles/ 1 second.
186,282 mi/s x 60s/1min x 60min/1hr x 24hrs/1day x 356days/1year = 5.87 x 1012 mi/yr
Kepler 186f: 490 Lyrs x 5.87 x 1012miles/ 1 Lyr = 2.88 x 1015 miles or 2.9 QUADRILLION MILES from Earth.
Just to put this distance into perspective, let’s suppose we utilize the fastest spacecraft we have to get there. The Voyager 1 spacecraft is moving at around 38,500 mi/hr. If we left on that craft today and headed towards this possible future Earth, it would take us roughly 8.5 MILLION YEARS to get there. That’s around 34 times longer than the time between when the first proto-humans began to appear on earth 250,000 years ago until today. So the entire history of human evolution from then till now replayed 34 times BEFORE you would arrive at this planet. Knowing these numbers, how is it even possible that we can know what this planet’s atmosphere, and others like it, are made of?
First, here’s a bit of chemistry in order for you to understand the field that is spectroscopy, and then how we apply it to the astronomical sciences. Different elements are composed of a differing number of protons, neutrons, and electrons. These varying numbers are what set the elements apart from one another on the periodic table. It is the electrons, however, that are of particular interest in the majority of what chemistry studies. These different electron configurations allow for what we call spectral signatures to exist among the elements. This means that since every single element has a specific electron configuration, the light that it both absorbs and emits acts as a sort of photon fingerprint; a unique identifier to that element.
A list of the elements with their corresponding visible light emission spectra. Image Credit: MIT Wavelength Tables, NIST Atomic Spectrum Database, umop.net
The standard equation for determining the characteristics of light is:
c= v λ
c is the speed of light in a vacuum (3.00 x 108 m/s)
v is the frequency of the light wave (in Hertz)
λ (lambda) represents the wavelength (in meters, but will usually be converted to nanometers) which will determine what color of light will be emitted from the element(s), or simply where the wavelength of light falls on the electromagnetic spectrum (infrared, visible, ultraviolet, etc.)
If you have either the frequency or the wavelength, you can determine the rest. You can even start with the energy of the light being detected by your instruments and then work backwards with the following equations:
The energy of a photon can be described mathematically as this:
Ephoton = hv
OR
Ephoton = h c / λ
What these mean is that the energy of a photon is the product of the frequency (v) of the light wave emitted multiplied by Planck’s Constant (h), which is 6.63 x 10-34 Joules x seconds. Or in the case of the second equation, the energy of the photon is equal to Planck’s Constant x the speed of light divided by the wavelength. This will give you the amount of energy that a specific wavelength of light contains. This equation is also known as the Planck-Einstein Relation. So, if you take a measurement and you are given a specific energy reading of the light coming from a distant star, you can then deduce what information you need about said light and determine which element(s) are either emitting or absorbing these wavelengths. It’s all mathematical detective work.
So, the electrons that orbit around the nucleus of atoms exist in what we call orbitals. Depending on the atom (and the electrons associated with it), there are many different orbitals. You have the “ground” orbital for the electron, which means that the electron(s) there are closest to the nucleus. They are “non-excited”. However, there are “higher” quantum orbitals that exist that the electron(s) can “jump” to when the atom is excited. Each orbital can have different quantum number values associated with it. The main value we will use is the Principle Quantum Number. This is denoted by the letter “n”, and has an assigned integer value of 1, 2, 3, etc. The higher the number, the further from the nucleus the electron resides, and the more energy is associated with it. This is best described with an example:
A hydrogen atom has 1 electron. That electron is whipping around its 1 proton nucleus in its ground state orbital. Suddenly, a burst of high energy light hits the hydrogen. This energy is transferred throughout the hydrogen atom, and the electron reacts. The electron will instantaneously “vanish” from the n1 orbital and then reappear on a higher quantum orbital (say n4). This means that as that light wave passed over this hydrogen atom, a specific wavelength was absorbed by the hydrogen (this is an important feature to remember for later).
Diagram of an electron dropping from a higher orbital to a lower one and emitting a photon. Image Credit: Wikimedia Commons
Eventually, the “excited” electron will drop from its higher quantum orbital (n4) back down to the n1 orbital. When this happens, a specific wavelength of light is emitted by the hydrogen atom. When the electron “drops”, it emits a photon of specific energy or wavelength (dependent upon many factors, including the state the electron was in prior to its “excitement”, the amount of levels the electron dropped, etc.) We can then measure this energy (or wavelength, or frequency,) to determine what element the photon is coming from (in this case, hydrogen). It is in this feature that each element has its own light signature. Each atom can absorb and emit specific wavelengths of light, and they are all tied together by the equations listed above.
So how does this all work? Well, in reality, there are many factors that go into this sort of astronomical study. I am simply describing the basic principle behind the work. I say this so that the many scientists that are doing this sort of work do not feel as though I have discredited their research and hard work; I promise you, it is painstakingly difficult and tedious and involves many more details that I am not mentioning here. That being said, the basic concept works like this:
We find a star that gives off the telltale signs that it has a planet orbiting around it. We do this with a few methods, but how it all first started was by detecting a “wobble” in the star’s apparent position. This “wobble” is caused by a planet orbiting around its parent star. You see, when a planet orbits a star (and when anything orbits anything else), the planet isn’t really orbiting the star, the planet AND the star are orbiting a common focal point. Usually with this type of orbital system, that common focal point is fairly close to the center of the star, and thus it’s safe to say that the planet orbits the star. However, this causes the star to move ever so slightly. We can measure this.
Once we determine that there are planets orbiting the star in question, we can study it more closely. When we do, we turn our instruments towards it and begin taking highly detailed measurements, and then we wait. What we are waiting for is a dimming of the star at a regular interval. What we are hoping for is this newly-found exoplanet to transit our selected star. When a planet transits a star, it moves in front of the star relative to us (this also means we are incredibly lucky, as not all planets will orbit “in front” of the star relative to our view). This will cause the star’s brightness to dip ever so slightly at a regular interval. Now we have identified a prime exoplanet candidate for study.
Diagram of how we can use absorption spectral reading to determine the atmosphere of an exoplanet. Image Credit: A. Feild, STScl, NASA
We can now introduce the spectroscopic principles to this hunt. We can take all sorts of measurements of the light that is coming from this star. Its brightness, the energy it’s kicking out per second, and even what that star is made of (the emission spectrum I discussed earlier). Then what we do is wait for the planet to transit the start, and begin taking readings. What we are doing is reading the light passing THROUGH the exoplanet’s atmosphere, and then studying what we can call an Absorption Spectrum reading. As I mentioned earlier, specific elements will absorb specific wavelengths of light. What we get back is a spectral reading of the star’s light signature (the emission spectra of the star), but with missing wavelengths that show up as very tiny black lines where there used to be color. These are called Fraunhofer lines, named after the “father” of astrophysics Joseph Fraunhofer, who discovered these lines in the 19th century.
The dark lines represent the light frequencies that were absorbed by specific chemicals that this particular light passed through. Image Credit: Wikimedia Commons
What we now have in our possession is a chemical fingerprint of what this exoplanet’s atmosphere is composed of. The star’s spectrum is splayed out before us, but the barcode of the planet’s atmospheric composition lay within the light. We can then take those wavelengths that are missing and compare them to the already established absorption/emission spectra of all of the known elements. In this way, we can begin to piece together what this planet has to offer us. If we get high readings of sulfur and hydrogen, we have probably just discovered a gas giant. However if we discover a good amount of nitrogen and oxygen, we may have found a world that has liquid water on its surface (provided that this planet resides within its host star’s “habitable” zone: a distance that is just far enough from the star to allow for liquid water). If we find a planet that has carbon dioxide in its atmosphere, we may just have discovered alien life (CO2 being a waste product of both cellular respiration and a lot of industrial processes, but it can also be a product of volcanism and other non-organic phenomena).
What this all means is that by being able to read the light from any given object, we can narrow our search for the next Earth. Regardless of distance, if we can obtain an accurate measurement of the light moving through an exoplanet’s atmosphere, we can tell what it is made of.
We have discovered some 2000 exoplanets thus far, and that number will only increase in the coming decades. With so many candidates, it will be a wonder if we do not find a planet that we humans can live on without the help of technology. Obviously our techniques will further be refined, and as new technologies, methods, and instruments become available, our ability to pinpoint planets that we can someday colonize will become increasingly more accurate.
With such telescopes like the James Webb Space Telescope launching soon, we will be able to image these exoplanets and get even better spectroscopic readings from them. This type of science is on the leading edge of humanity’s journey into the cosmos. Astrophysicists and astrochemists that work in this field are the necessary precursors to the brave men and women who will one day board those interstellar spacecraft and launch our civilization into the Universe to truly become an interstellar species.
Possible glimpse into our future… Image Credit: Battlestar Wiki Media
Artist’s impression of how an an Earth-like exoplanet might look. Credit: ESO.
The search for worlds beyond our own is one of humankind’s greatest quests. Scientists have found thousands of exoplanets orbiting other stars in the Milky Way, but are still ironing out the details of what factors truly make a planet habitable. But thanks to researchers at Cornell University, their search may become a little easier. A team at the Institute for Pale Blue Dots has zeroed in on the range of habitable orbits for very young Earth-like planets, giving astronomers a better target to aim at when searching for rocky worlds that contain liquid water and could support the evolution of life.
The Habitable Zone (HZ) of a star is its so-called “Goldilocks region,” the not-too-hot, not-too-cold belt within which liquid water could exist on orbiting rocky planets. Isolating planets in the HZ is the primary objective for scientists hoping to find evidence of life. Until now, astronomers have mainly been searching for worlds that lie in the HZ of stars that are in the prime of their lives: those that are on the Main Sequence, the cosmic growth chart for stellar evolution. According to the group at Cornell, however, scientists should also be looking at cooler, younger stars that have not yet reached such maturity.
The increased distance of the Habitable Zone from pre-main sequence stars makes it easier to spot infant Earths. Credit: Astrophysical Journal Letters.
As shown in the figure above, cool stars in classes F, G, K, and M are more luminous in their pre-Main Sequence stage than they are once they mature. Planets that circle around such bright stars tend to have more distant orbits than those that accompany dimmer stars, making transits more visible and providing a larger HZ for astronomers to probe. In addition, the researchers found that fledgling planets can spend up to 2.5 billion years in the HZ of a young M-class star, a period of time that would allow ample time for life to flourish.
But just because liquid water could exist on a planet doesn’t mean that it does. A rocky planet must first acquire water, and then retain it long enough for life to develop. The Cornell group found that a watery world could lose its aqueous environment to a runaway greenhouse effect if if forms too close to a cool parent star, even if the planet was on course to eventually stray into the star’s HZ. These seemingly habitable planets would have to receive a second supply of water later on in order to truly support life. “Our own planet gained additional water after this early runaway phase from a late, heavy bombardment of water-rich asteroids,” offered Ramses Ramirez, one author of the study. “Planets at a distance corresponding to modern Earth or Venus orbiting these cool stars could be similarly replenished later on.”
Estimations for the HZs of cool, young stars and probable amounts of water loss for exoplanets orbiting at various distances are provided in a preprint of the paper, available here. The research will be published in the January 1, 2015, issue of The Astrophysical Journal.
Artist’s impression of the deep blue planet HD 189733b, based on observations from the Hubble Space Telescope. Credit: NASA/ESA.
If you think exoplanet detections are only in the realm of professional planet-hunting telescopes such as Kepler, take a look at the video above. David Schneider, a senior editor for IEEE Spectrum, explains that it takes little more than a DSLR camera and a camera lens to catch a glimpse.
Schneider told Universe Today that he’s not an experienced amateur observer, nor should his equipment be expected to detect new exoplanets. But the potential for the future is interesting, he explained.
“I was simply trying to detect the signature of a known exoplanet, one that was discovered years ago with far more sophisticated gear,” he wrote in an e-mail. “I knew exactly which star to look at, when the transit occurs, and what the change in brightness would be. I relied on the expertise of professional astronomers to provide all that information.”
Here’s the setup: a Canon EOS Rebel XS DSLR, a 300-millimeter Nikon telephoto lens, an adapter to get the Nikon talking to the Canon, and a self-built “barn door tracker” that he constructed based on descriptions he found on the web. (His IEEE Spectrum article has more details.)
Schneider chose HD 189733, whose hostile-to-life “deep blue” exoplanet is about 63 light-years away and transits the face of the star every 2.2 days. But often these transits take place at inconvenient times (such as during the day, and the star is low on the horizon). He also faced several cloudy nights, meaning it was several weeks until he could take the imagery.
Once that was finished, Schneider ran the pictures through a piece of astronomical imaging software called Iris. In Schneider’s words, this is how the software helped him pick out the planet:
At the most basic level, Iris allows you to perform the corrections that are customary for really all types of digital astrophotography. In particular, you correct for ‘hot pixels’ in your camera sensor and for variations in the sensitivity of the sensor across the frame. This is standard stuff in astrophotography, requiring that you take images with the lens cap on (so-called “darks”), of a uniformly illuminated background (“flats”), and so forth.
For this project, you also need to use the tools that Iris provides to do what’s called aperture photometry. In a nutshell, you have to adjust the registration of the set of images you collect so that the stars are in the same position in each image. Then you have to set up things in Iris to do photometric measurements of a selected set of stars in one frame. After that, Iris will perform the photometry you want on the whole set of images you have in an automated fashion.
While his equipment isn’t sophisticated enough to account for “false positives” such as a sunspot going across a star — amateurs are more at the stage of confirming professional observations — Schneider pointed out there are many similar projects to his own. Among them are KELT-NORTH (which inspired his search), Evryscope, and this group at the University of Arizona.
“My project merely highlights that you can get your feet wet in this area with some really cheap hardware,” Schneider said. He recommends those that want to do similar work to his read the IEEE Spectrum article, buy the hardware required, read up on astrophotography and Iris, and not be afraid to experiment.
Schneider added he wasn’t trying to do “anything special” — many amateurs have encountered similar success — but he had a lot of fun. “Maybe because I’m a bit of a computer nerd, I found digital astrophotography to be a lot more enjoyable than actually looking through a telescope, which in the few times I’ve done that often involved a lot of squinting and unpleasant vibration.”
A new research paper reveals more details of the effect gamma ray bursts (GRB) have had on the development of complex life throughout the cosmos. Illustration depicts a beam from a GRB as might have been directed toward early life on Earth during the Cambrian or Ordovician periods, ~500 million years ago. (Illustration Credit: T. Reyes)
If too close to an environment harboring complex life, a gamma ray burst could spell doom for that life. But could GRBs be the reason we haven’t yet found evidence of other civilizations in the cosmos? To help answer the big question of “where is everybody?” physicists from Spain and Israel have narrowed the time period and the regions of space in which complex life could persist with a low risk of extinction by a GRB.
GRBs are some of the most cataclysmic events in the Universe. Astrophysicists are astounded by their intensity, some of which can outshine the whole Universe for brief moments. So far, they have remained incredible far-off events. But in a new paper, physicists have weighed how GRBs could limit where and when life could persist and evolve, potentially into intelligent life.
In their paper, “On the role of GRBs on life extinctions in the Universe”, published in the journal Science, Dr. Piran from Hebrew University and Dr. Jimenez from University of Barcelona consider first what is known about gamma ray bursts. The metallicity of stars and galaxies as a whole are directly related to the frequency of GRBs. Metallicity is the abundance of elements beyond hydrogen and helium in the content of stars or whole galaxies. More metals reduce the frequency of GRBs. Galaxies that have a low metal content are prone to a higher frequency of GRBs. The researchers, referencing their previous work, state that observational data has shown that GRBs are not generally related to a galaxy’s star formation rate; forming stars, including massive ones is not the most significant factor for increased frequency of GRBs.
As fate would have it, we live in a high metal content galaxy – the Milky Way. Piran and Jimenez show that the frequency of GRBs in the Milky Way is lower based on the latest data available. That is the good news. More significant is the placement of a solar system within the Milky Way or any galaxy.
The brightest gamma-ray burst ever seen in X-rays temporarily blinded Swift’s X-ray Telescope on 21 June 2010. This image merges the X-rays (red to yellow) with the same view from Swift’s Ultraviolet/Optical Telescope, which showed nothing extraordinary. Credit: NASA/Swift/Stefan Immler
The paper states that there is a 50% chance of a lethal GRB’s having occurred near Earth within the last 500 million years. If a stellar system is within 13,000 light years (4 kilo-parsecs) of the galactic center, the odds rise to 95%. Effectively, this makes the densest regions of all galaxies too prone to GRBs to permit complex life to persist.
The Earth lies at 8.3 kilo-parsecs (27,000 light years) from the galactic center and the astrophysicists’ work also concludes that the chances of a lethal GRB in a 500 million year span does not drop below 50% until beyond 10 kilo-parsecs (32,000 light years). So Earth’s odds have not been most favorable, but obviously adequate. Star systems further out from the center are safer places for life to progress and evolve. Only the outlying low star density regions of large galaxies keep life out of harm’s way of gamma ray bursts.
The paper continues by describing their assessment of the effect of GRBs throughout the Universe. They state that only approximately 10% of galaxies have environments conducive to life when GRB events are a concern. Based on previous work and new data, galaxies (their stars) had to reach a metallicity content of 30% of the Sun’s, and the galaxies needed to be at least 4 kilo-parsecs (13,000 light years) in diameter to lower the risk of lethal GRBs. Simple life could survive repeated GRBs. Evolving to higher life forms would be repeatedly set back by mass extinctions.
Piran’s and Jimenez’s work also reveals a relation to a cosmological constant. Further back in time, metallicity within stars was lower. Only after generations of star formation – billions of years – have heavier elements built up within galaxies. They conclude that complex life such as on Earth – from jelly fish to humans – could not have developed in the early Universe before Z > 0.5, a cosmological red-shift equal to ~5 billion years ago or longer ago. Analysis also shows that there is a 95% chance that Earth experienced a lethal GRB within the last 5 billion years.
The question of what effect a nearby GRB could have on life has been raised for decades. In 1974, Dr. Malvin Ruderman of Columbia University considered the consequences of a nearby supernova on the ozone layer of the Earth and on terrestrial life. His and subsequent work has determined that cosmic rays would lead to the depletion of the ozone layer, a doubling of the solar ultraviolet radiation reaching the surface, cooling of the Earth’s climate, and an increase in NOx and rainout that effects biological systems. Not a pretty picture. The loss of the ozone layer would lead to a domino effect of atmospheric changes and radiation exposure leading to the collapse of ecosystems. A GRB is considered the most likely cause of the mass extinction at the end of the Ordovician period, 450 million years ago; there remains considerable debate on the causes of this and several other mass extinction events in Earth’s history.
The paper focuses on what are deemed long GRBs – lGRBs – lasting several seconds in contrast to short GRBs which last only a second or less. Long GRBs are believed to be due to the collapse of massive stars such as seen in supernovas, while sGRBs are from the collision of neutron stars or black holes. There remains uncertainty as to the causes, but the longer GRBs release far greater amounts of energy and are most dangerous to ecosystems harboring complex life.
The paper narrows the time and space available for complex life to develop within our Universe. Over the age of the Universe, approximately 14 billion years, only the last 5 billion years have been conducive to the creation of complex life. Furthermore, only 10% of the galaxies within the last 5 billion years provided such environments. And within only larger galaxies, only the outlying areas provided the safe distances needed to evade lethal exposure to a gamma ray burst.
This work reveals how well our Solar System fits within the ideal conditions for permitting complex life to develop. We stand at a fairly good distance from the Milky Way’s galactic center. The age of our Solar System, at approximately 4.6 billion years, lies within the 5 billion year safe zone in time. However, for many other stellar systems, despite how many are now considered to exist throughout the Universe – 100s of billions in the Milky Way, trillions throughout the Universe – simple is probably a way of life due to GRBs. This work indicates that complex life, including intelligent life, is likely less common when just taking the effect of gamma ray bursts into consideration.
Artist's conception of binary Earths. Credit: NASA
One big driver in the search for exoplanets is whether life can exist elsewhere in the Universe. In fact, a major goal of the Kepler space telescope is to discover an Earth-like planet in the habitable zone of a star like our Sun.
But what about having two Earths orbiting close to each other for billions of years? Is this even possible? A new study suggests that yes, this could happen. Imagine the implications for planetary searches if a double Earth is possible.
With current technology it’s hard to spot an Earth-sized planet, let alone resolve two, but if such planets exist it presents interesting questions. Could they be habitable? How do they form? More study is needed.
The study says double Earths can happen if they form at least half a Sun-Earth distance from their star. In what scientists say is the first-ever study considering binary Earths they suggest a scenario where two rocky bodies get close to each other early in their Solar System’s formation. They don’t collide (such as what likely formed our Moon), but they’re close enough to be within three or so radii of each other.
Artist’s conception of two celestial bodies smacking into each other. Such a collision is believed to have formed Earth’s moon. Credit: NASA/JPL-Caltech
“There is a good reason to believe terrestrial binary planetary systems may be possible,” read a press release from the California Institute of Technology. “In a grazing collision the angular momentum is too high to be contained within a single rotating body (it would fission) and if the bodies barely touch then they could retain their identity. However, it requires an encounter where the bodies are initially approaching each other at low enough velocity.”
Scientists simulated these planetary encounters using a simulation, dubbed Smooth Particle Hydrodynamics, which has been used in the past for scenarios such as the collision that created the Moon. The scenarios showed that a collision between two Earth-sized planets would only produce a Moon. However, if the bodies came close enough to produce tidal distortion on each other, the planets could form a binary system.
The research was presented at the Division for Planetary Sciences meeting of the American Astronomical Society this week by undergraduate Keegan Ryan, graduate student Miki Nakajima, and planetary science researcher David Stevenson, all of the California Institute of Technology. A press release did not disclose plans for publication, or if the research is peer-reviewed.
Artist's conception of early planetary formation from gas and dust around a young star. Outbursts from newborn and adolescent stars might drive planetary water beneath the surface of rocky worlds.
Credit: NASA/NASA/JPL-Caltech
This isn’t a clone of our Solar System, but it’s close enough. Scientists eagerly scrutinized a young star system called HD 95086 to learn more about how dust belts and giant planets grow up together. This is an important finding for our own neighborhood, where the gas giants of Jupiter, Saturn, Uranus and Neptune are also wedged between dusty areas.
“By looking at other star systems like these, we can piece together how our own Solar System came to be,” stated lead author Kate Su, an associate astronomer at the University of Arizona, Tucson.
The system is about 295 light-years from Earth, and is suspected to have two dust belts: a warmer one (similar to our asteroid belt) and a cooler one (similar to the Kuiper Belt that has icy objects.) The system is host to at least one planet that is five times the mass of Jupiter, and other planets could also be hiding between the dusty lanes. This planet, called HD 95086 b, was imaged by the European Southern Observatory’s Very Large Observatory in 2013.
Planet HD95086 b is shown at lower left in this picture. Astronomers blocked out the light of the star (center) to image the exoplanet. The blue circle represents the equivalent orbit of Neptune in this star system. Credit: ESO/J. Rameau
The next step was a comparison study with another star system called HR 8799, which also has two dusty rings and in this case, at least four planets in between. These planets have also been caught on camera. Comparing the structure of the two systems indicates that HD 95086 may have more planets lurking for astronomers to discover.
“By knowing where the debris is, plus the properties of the known planet in the system, we can get an idea of what other kinds of planets can be there,” stated Sarah Morrison, a co-author of the paper and a PhD student at the University of Arizona. “We know that we should be looking for multiple planets instead of a single giant planet.”
The researchers presented their work at the Division for Planetary Science Meeting of the American Astronomical Society in Tucson, Arizona. A press release did not disclose publication plans or if the work was peer-reviewed.
This is the sharpest image ever taken by ALMA — sharper than is routinely achieved in visible light with the NASA/ESA Hubble Space Telescope. It shows the protoplanetary disc surrounding the young star HL Tauri. These new ALMA observations reveal substructures within the disc that have never been seen before and even show the possible positions of planets forming in the dark patches within the system. Credit: ALMA (ESO/NAOJ/NRAO)
In a test of its new high resolution capabilities, the Atacama Large Millimeter/submillimeter Array (ALMA) is happily sharing some family snapshots with us. Astronomers manning the cameras have captured one of the best images so far of a newly-forming planet system gathering itself around a recently ignited star. Located about 450 light years from us in the constellation of Taurus, young HL Tau gathers material around it to hatch its planets and fascinate researchers.
Thanks to ALMA images, scientists have been able to witness stages of planetary formation which have been suspected, but never visually confirmed. This very young star is surrounded by several concentric rings of material which have neatly defined spacings. Is it possible these clearly marked gaps in the solar rubble disc could be where planets have started to gel?
“These features are almost certainly the result of young planet-like bodies that are being formed in the disk. This is surprising since HL Tau is no more than a million years old and such young stars are not expected to have large planetary bodies capable of producing the structures we see in this image,” said ALMA Deputy Director Stuartt Corder.
“When we first saw this image we were astounded at the spectacular level of detail. HL Tauri is no more than a million years old, yet already its disc appears to be full of forming planets. This one image alone will revolutionize theories of planet formation,” explained Catherine Vlahakis, ALMA Deputy Program Scientist and Lead Program Scientist for the ALMA Long Baseline Campaign.
Let’s take a look at what we understand about solar system formation…
Through repeated research, astronomers suspect that all stars are created when clouds of dust and gas succumb to gravity and collapse on themselves. As the star begins to evolve, the dust binds together – turning into “solar system soup” consisting of an array of different sized sand and rocks. This rubble eventually congeals into a thin disc surrounding the parent star and becomes home to newly formed asteroids, comets, and planets. As the planets collect material into themselves, their gravity re-shapes to structure of the disc which formed them. Like dragging a lawn sweeper over fallen leaves, these planets clear a path in their orbit and form gaps. Eventually their progress pulls the gas and dust into an even tighter and more clearly defined structure. Now ALMA has shown us what was once only a computer model. Everything we thought we knew about planetary formation is true and ALMA has proven it.
This is the sharpest image ever taken by ALMA — sharper than is routinely achieved in visible light with the NASA/ESA Hubble Space Telescope. It shows the protoplanetary disc surrounding the young star HL Tauri. The observations reveal substructures within the disc that have never been seen before and even show the possible positions of planets forming in the dark patches within the system. In this picture the features seen in the HL Tauri system are labelled. Credit: ALMA (ESO/NAOJ/NRAO)
“This new and unexpected result provides an incredible view of the process of planet formation. Such clarity is essential to understand how our own solar system came to be and how planets form throughout the universe,” said Tony Beasley, director of the National Radio Astronomy Observatory (NRAO) in Charlottesville, Virginia, which manages ALMA operations for astronomers in North America.
“Most of what we know about planet formation today is based on theory. Images with this level of detail have up to now been relegated to computer simulations or artist’s impressions. This high resolution image of HL Tauri demonstrates what ALMA can achieve when it operates in its largest configuration and starts a new era in our exploration of the formation of stars and planets,” says Tim de Zeeuw, Director General of ESO.
The major reason astronomers have never seen this type of structure before is easy to envision. The very dust which creates the planetary disc around HL Tau also conceals it to visible light. Thanks to ALMA’s ability to “see” at much longer wavelengths, it can image what’s going on at the very heart of the cloud. “This is truly one of the most remarkable images ever seen at these wavelengths. The level of detail is so exquisite that it’s even more impressive than many optical images. The fact that we can see planets being born will help us understand not only how planets form around other stars but also the origin of our own solar system,” said NRAO astronomer Crystal Brogan.
How does ALMA do it? According to the research staff, its new high-resolution capabilities were achieved by spacing the antennas up to 15 kilometers apart. This baseline at millimeter wavelengths enabled a resolution of 35 milliarcseconds, which is equivalent to a penny as seen from more than 110 kilometers away. “Such a resolution can only be achieved with the long baseline capabilities of ALMA and provides astronomers with new information that is impossible to collect with any other facility, including the best optical observatories,” noted ALMA Director Pierre Cox.
This is a composite image of the young star HL Tauri and its surroundings using data from ALMA (enlarged in box at upper right) and the NASA/ESA Hubble Space Telescope (rest of the picture). This is the first ALMA image where the image sharpness exceeds that normally attained with Hubble. Credit: ALMA (ESO/NAOJ/NRAO)
The long baselines spell success for the ALMA observations and are a tribute to all the technology and engineering that went into its construction. Future observations at ALMA’s longest possible baseline of 16 kilometers will mean even more detailed images – and an opportunity to further expand our knowledge of the Cosmos and its workings. “This observation illustrates the dramatic and important results that come from NSF supporting world-class instrumentation such as ALMA,” said Fleming Crim, the National Science Foundation assistant director for Mathematical and Physical Sciences. “ALMA is delivering on its enormous potential for revealing the distant universe and is playing a unique and transformational role in astronomy.”
Pass them baby pictures our way, Mama ALMA… We’re delighted to take a look!
This wide-field view shows the sky around the young multiple star system GG Tauri, which appears very close to the centre of this picture. This view also shows a dust cloud and evidence of star formation near the top of the picture. Credit: ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin
Deep within the Taurus Dark Cloud complex, one of the closest star-forming regions to Earth has just revealed one of its secrets – an umbilical cord of gas flowing from the expansive outer disc toward the interior of a binary star system known as GG Tau-A. According to the ESO press release, this never-before-seen feature may be responsible for sustaining a second, smaller disc of planet-forming material that otherwise would have disappeared long ago.
A research group led by Anne Dutrey from the Laboratory of Astrophysics of Bordeaux, France and CNRS used the Atacama Large
Millimeter/submillimeter Array (ALMA) to observe the distribution of
dust and gas in the unusual GG Tau-A system. Since at least half of
Sun-like stars are the product of binary star systems, these type of
findings may produce even more fertile grounds for discovering
exoplanets. However, the 450 light year distant GG Tau system is even more complex than previously thought. Through observations taken with the VLTI, astronomers have discovered its primary star – home to the inner disc – is part of a more involved multiple-star system. The secondary star is also a close binary!
“We may be witnessing these types of exoplanetary systems in the midst of formation,” said Jeffrey Bary, an astronomer at Colgate University in Hamilton, N.Y., and co-author of the paper. “In a sense, we are learning why these seemingly strange systems exist.”
Let’s take a look…
This artist’s impression shows the dust and gas around the double star system GG Tauri-A. Researchers using ALMA have detected gas in the region between two discs in this binary system. This may allow planets to form in the gravitationally perturbed environment of the binary. Half of Sun-like stars are born in binary systems, meaning that these findings will have major consequences for the hunt for exoplanets.
“Like a wheel in a wheel, GG Tau-A contains a large, outer disc
encircling the entire system as well as an inner disc around the main central star. This second inner disc has a mass roughly equivalent to that of Jupiter.” says the research team. “Its presence has been an intriguing mystery for astronomers since it is losing material to its central star at a rate that should have depleted it long ago.”
Thanks to studies done with ALMA, the researchers made an exciting discovery in these disc structures… gas clumps located between the two. This observation could mean that material is being fed from the outer disc to feed the inner. Previously observations done with ALMA show that a single star pulls its materials inward from the outer disc. Is it possible these gas pockets in the double disc GG Tau-A system are creating a sustaining lifeline between the two?
“Material flowing through the cavity was predicted by computer
simulations but has not been imaged before. Detecting these clumps
indicates that material is moving between the discs, allowing one to
feed off the other,” explains Dutrey. “These observations demonstrate that material from the outer disc can sustain the inner disc for a long time. This has major consequences for potential planet formation.”
As we know, planets are created from the materials leftover from
stellar ignition. However, the creation of a solar system occurs at a snail’s pace, meaning that a debris disc with longevity is required for planet formation. Thanks to these new “disc feeding” observations from ALMA, researchers can surmise that other multiple-star systems behave in a similar manner… creating even more possibilities for exoplanet formation.
“This means that multiple star systems have a way to form planets, despite their complicated dynamics. Given that we continue to find interesting planetary systems, our observations provide a glimpse of the mechanisms that enable such systems to form,” concludes Bary.
During the initial phase of planetary searches, the emphasis was placed on Sun-like, single-host stars. Later on, binary systems gave rise to giant Jupiter-sized planets – nearly large enough to be stars on their own. Now the focus has turned to pointing our planetary discovery efforts towards individual members of multiple-systems.
Emmanuel Di Folco, co-author of the paper, concludes: “Almost half the Sun-like stars were born in binary systems. This means that we have found a mechanism to sustain planet formation that applies to a significant number of stars in the Milky Way. Our observations are a big step forward in truly understanding planet formation.”
