Alpha Centauri is the closest star system to us, at 4.37 light-years (about 25 trillion miles) away. In 2016, astronomers discovered an exoplanet orbiting one of the three stars in the Alpha Centauri system. Spurred on by that discovery, the European Southern Observatory (ESO) has developed a new instrument to find any other planets that might be in the Alpha Centauri system, and it’s busy looking right now.Continue reading “New Instrument is Searching for Planets Around Alpha Centauri”
In August of 2016, astronomers from the European Southern Observatory (ESO) announced the discovery of an exoplanet in the neighboring system of Proxima Centauri. The news was greeted with consider excitement, as this was the closest rocky planet to our Solar System that also orbited within its star’s habitable zone. Since then, multiple studies have been conducted to determine if this planet could actually support life.
Unfortunately, most of the research so far has indicated that the likelihood of habitability are not good. Between Proxima Centauri’s variability and the planet being tidally-locked with its star, life would have a hard time surviving there. However, using lifeforms from early Earth as an example, a new study conducted by researchers from the Carl Sagan Institute (CSI) has shows how life could have a fighting chance on Proxima b after all.Continue reading “The Closest Star to the Sun, Proxima Centauri, has a Planet in the Habitable Zone. Life Could be There Right Now”
In of August of 2016, astronomers from the European Southern Observatory (ESO) confirmed the existence of an Earth-like planet around Proxima Centauri – the closest star to our Solar System. In addition, they confirmed that this planet (Proxima b) orbited within its star’s habitable zone. Since that time, multiple studies have been conducted to determine if Proxima b could in fact be habitable.
Unfortunately, most of this research has not been very encouraging. For instance, many studies have indicated that Proxima b’s sun experiences too much flare activity for the planet to sustain an atmosphere and liquid water on its surface. However, in a new NASA-led study, a team of scientists has investigated various climate scenarios that indicate that Proxima b could still have enough water to support life.
At distance of just 4.367 light years, the triple star system of Alpha Centauri (Alpha Centauri A+B and Proxima Centauri) is the closest star system to our own. In 2016, researchers from the European Southern Observatory announced the discovery of Proxima b, a rocky planet located within the star’s habitable zone and the closest exoplanet to our Solar System. However, whether or not Alpha Centauri has any potentially habitable planets remains a mystery.
Between 2012 and 2015, three possible candidates were announced in this system, but follow-up studies cast doubt on their existence. Looking to resolve this mystery, Tom Ayres – a senior research associate and Fellow at the University of Colorado Boulder’s Center for Astrophysics and Space Astronomy – conducted a study of Alpha Centauri based on over a decade’s worth of observations, with encouraging results!
The results of this study were presented at the 232rd meeting of the American Astronomical Society, which took place in Denver, Colorado, from June 3rd to June 7th. The study was based on ten years worth of monitoring of Alpha Centauri, which was provided the Chandra X-ray Observatory. This data indicated that any planets that orbit Alpha Centauri A and B are not likely to be bombarded by large amounts of X-ray radiation.
This is good news as far as Alpha Centauri’s potential habitability goes since X-rays and related Space Weather effects are harmful to unprotected life. Not only can high doses of radiation be lethal to living creatures, they can also strip away planetary atmospheres. According to data provided by the Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter, this is precisely what happened to Mars between 4.2 and 3.7 billion years ago.
As Tom Ayres explained in a recent Chandra press release:
“Because it is relatively close, the Alpha Centauri system is seen by many as the best candidate to explore for signs of life. The question is, will we find planets in an environment conducive to life as we know it?”
The stars in the Alpha Centauri system (A and B) are quite similar to our Sun and orbit relatively close to each other. Alpha Centauri A, a G2 V (yellow dwarf) star, is the most Sun-like of the two, being 1.1 times the mass and 1.519 times the luminosity of the Sun. Alpha Centauri B is somewhat smaller and cooler, at 0.907 times the Sun’s mass and 0.445 times its visual luminosity.
As such, the odds that the system could support an Earth-like planet are pretty good, especially around Alpha Centauri A. According to the Chandra data, the prospects for life (based on X-ray bombardment) are actually better for any planet orbiting Alpha Centauri A than for the Sun, and Alpha Centauri B is only slightly worse. This is certainly good news for those who are hoping that a potentially habitable exoplanet is found in close proximity to the Solar System.
When the existence of Proxima b was first announced, there was naturally much excitement. Not only did this planet orbit within it’s star’s habitable zone, but it was the closest known exoplanet to Earth. Subsequent studies, however, revealed that Proxima Centauri is variable and unstable by nature, which makes it unlikely that Proxima b could maintain an atmosphere or life on its surface. As Ayers explained:
“This is very good news for Alpha Cen AB in terms of the ability of possible life on any of their planets to survive radiation bouts from the stars. Chandra shows us that life should have a fighting chance on planets around either of these stars.”
Meanwhile, astronomers continue to search for exoplanets around Alpha Centauri A and B, but without success. The problem with this system is the orbit of the pair, which has drawn the two bright stars close together in the sky over the past decade. To help determine if Alpha Centauri was hospitable to life, astronomers began conducting a long-term observation campaign with Chandra in 2005.
As the only X-ray observatory capable of resolving Alpha Centauri A and B during its current close orbital approach, Chandra observed these two main stars every six months for the past thirteen years. These long-term measurements captured a full cycle of increases and decreases in X-ray activity, in much the same way that the Sun has an 11-year sunspot cycle.
What these observations showed was that any planet orbiting within the habitable zone of A would receive (on average) a lower dose of X-rays compared to similar planets around the Sun. For planets orbiting withing the habitable zone of B, the X-ray dose they received would be about five times higher. Meanwhile, planets orbiting within Proxima Centauri’s habitable zone would get an average of 500 times more X-rays, and 50,000 times more during a big flare.
In addition to providing encouraging hints about Alpha Centauri’s possible habitability, the X-ray observations provided by Chandra could also go a long way towards informing astronomers about our Sun’s X-ray activity. Understanding this is key to learning more about space weather and the threat they can pose to human infrastructure, as well as other technologically-advanced civilizations.
In the meantime, astronomers continue to search for exoplanets around Alpha Centauri A and B. Knowing that they have a good chance of supporting life will certainly make any future exploration of this system (like Project Starshot) all the more lucrative!
Some of the study’s results also appeared in the January issue in the Research Notes of the American Astronomical Society, titled “Alpha Centauri Beyond the Crossroads“. And be sure to enjoy this video about Alpha Centauri’s potential habitability, courtesy of the Chandra X-ray Observatory:
Further Reading: Chandra X-ray Observatory
Since its discovery was announced in August of 2016, Proxima b has been an endless source of wonder and the target of many scientific studies. In addition to being the closest extra-solar planet to our Solar System, this terrestrial planet also orbits within Proxima Centauri’s circumstellar habitable zone (aka. “Goldilocks Zone”). As a result, scientists have naturally sought to determine if this planet could actually be home to extra-terrestial life.
Many of these studies have been focused on whether or not Proxima b could retain an atmosphere and liquid water on its surface in light of the fact that it orbits an M-type (red dwarf) star. Unfortunately, many of these studies have revealed that this is not likely due to flare activity. According to a new study by an international team of scientists, Proxima Centauri released a superflare that was so powerful, it would have been lethal to any life as we know it.
The study, titled “The First Naked-Eye Superflare Detected from Proxima Centauri“, recently appeared online. The team was led by Howard Ward, a PhD candidate in physics and astronomy at the UNC Chapel Hill, with additional members from the NASA Goddard Space Flight Center, the University of Washington, the University of Colorado, the University of Barcelona and the School of Earth and Space Exploration at Arizona State University.
As they indicate in their study, solar flare activity would be one of the greatest potential threats to planetary habitability in a system like Proxima Centauri. As they explain:
“[W]hile ozone in an Earth-like planet’s atmosphere can shield the planet from the intense UV flux associated with a single superflare, the atmospheric ozone recovery time after a superflare is on the order of years. A sufficiently high flare rate can therefore permanently prevent the formation of a protective ozone layer, leading to UV radiation levels on the surface which are beyond what some of the hardiest-known organisms can survive.”
In addition stellar flares, quiescent X-ray emissions and UV flux from a red dwarf star can would be capable of stripping planetary atmospheres over the course of several billion years. And while multiple studies have been conducted that have explored low- and moderate-energy flare events on Proxima, only one high-energy event has even been observed.
This occurred on March of 2016, when Proxima Centauri emitted a superflare that was so bright, it was visible to the naked eye. This flare was observed by the Evryscope, an array of telescopes – funded through the National Science Foundation‘s Advanced Technologies and Instrumentation (ATI) and Faculty Early Career Development (CAREER) programs – that is pointed at every part of the accessible sky simultaneously and continuously.
As the team indicates in their study, the March 2016 superflare was the first to be observered from Proxima Centauri, and was rather powerful:
“In March 2016 the Evryscope detected the first-known Proxima superflare. The superflare had a bolometric energy of 10^33.5 erg, ~10× larger than any previously-detected flare from Proxima, and 30×larger than any optically measured Proxima flare. The event briefly increased Proxima’s visible-light emission by a factor of 38× averaged over the Evryscope’s 2-minute cadence, or ~68× at the cadence of the human eye. Although no M-dwarfs are usually visible to the naked-eye, Proxima briefly became a magnitude-6.8 star during this superflare, visible to dark-site naked-eye observers.”
The superflare coincided with the three-month Pale Red Dot campaign, which was responsible for first revealing the existence of Proxima b. While monitoring the star with the HARPS spectrograph – which is part of the 3.6 m telescope at the ESO’s La Silla Observatory in Chile – the campaign team also obtaining spectra on March 18th, 08:59 UT (just 27 minutes after the flare peaked at 08:32 UT).
The team also noted that over the last two years, the Evryscope has recorded 23 other large Proxima flares, ranging in energy from 10^30.6 erg to 10^32.4 erg. Coupled with rates of a single superflare detection, they predict that at least five superflares occur each year. They then combined this data with the high-resolution HARPS spectroscopy to constrain the superflare’s UV spectrum and any associated coronal mass ejections.
The team then used the HARPS spectra and the Evryscope flare rates to create a model to determine what effects this star would have on a nitrogen-oxygen atmosphere. This included how long the planet’s protective ozone layer would be able to withstand the blasts, and what effect regular exposure to radiation would have on terrestrial organisms.
“[T]he repeated flaring is sufficient to reduce the ozone of an Earth-like atmosphere by 90% within five years. We estimate complete depletion occurs within several hundred kyr. The UV light produced by the Evryscope superflare therefore reached the surface with ~100× the intensity required to kill simple UV-hardy microorganisms, suggesting that life would struggle to survive in the areas of Proxima b exposed to these flares.”
Essentially, this and other studies have concluded that any planets orbiting Proxima Centauri would not be habitable for very long, and likely became lifeless balls of rock a long time ago. But beyond our closest neighboring star system, this study also has implications for other M-type star systems. As they explain, red dwarf stars are the most common in our galaxy – roughly 75% of the population – and two-thirds of these stars experience active flare activity.
As such, measuring the impact that superflares have on these worlds will be a necessary component to determining whether or not exoplanets found by future missions are habitable. Looking ahead, the team hopes to use the Evryscope to examine other star systems, particularly those that are targets for the upcoming Transiting Exoplanet Survey Satellite (TESS) mission.
“Beyond Proxima, Evryscope has already performed similar long-term high-cadence monitoring of every other Southern TESS planet-search target, and will therefore be able to measure the habitability impact of stellar activity for all Southern planetsearch-target M-dwarfs,” they write. “In conjunction with coronal-mass-ejection searches from long- wavelength radio arrays like the [Long Wavelength Array], the Evryscope will constrain the long-term atmospheric effects of this extreme stellar activity.”
For those who hoped that humanity might find evidence of extra-terrestrial life in their lifetimes, this latest study is certainly a letdown. It’s also disappointing considering that in addition to being the most common type of star in the Universe, some research indicates that red dwarf stars may be the most likely place to find terrestrial planets. However, even if two-thirds of these stars are active, that still leaves us with billions of possibilities.
It is also important to note that these studies help ensure that we can determine which exoplanets are potentially habitable with greater accuracy. In the end, that will be the most important factor when it comes time to decide which of these systems we might try to explore directly. And if this news has got you down, just remember the worlds of the immortal Carl Sagan:
“The universe is a pretty big place. If it’s just us, seems like an awful waste of space.”
Further Reading: arXiv
Since it’s discovery was announced in August of 2016, Proxima b has been an endless source of wonder and the target of many scientific studies. As the closest extra-solar planet to our Solar System – and a terrestrial planet that orbits within Proxima Centauri’s circumstellar habitable zone (aka. “Goldilocks Zone”) – scientists have naturally wondered whether or not this planet could be habitable.
Unfortunately, many of these studies have emphasized the challenges that life on Proxima b would likely face, not the least of which is harmful radiation from its star. According to a recent study, a team of astronomers used the ALMA Observatory to detect a large flare emanating from Proxima Centauri. This latest findings, more than anything, raises questions about how habitable its exoplanet could be.
The study, titled “Detection of a Millimeter Flare from Proxima Centauri“, recently appeared in The Astrophysical Journal Letters. Led by Meredith A. MacGregor, an NSF Astronomy and Astrophysics Postdoctoral Fellow at the Carnegie Institution for Science, the team also included members from the Harvard-Smithsonian Center for Astrophysics (CfA) and the University of Colorado Boulder.
For the sake of their study, the team used data obtained by the Atacama Large Millimeter/submillimeter Array (ALMA) between January 21st to April 25th, 2017. This data revealed that the star underwent a significant flaring event on March 24th, where it reached a peak that was 1000 times brighter than the star’s quiescent emission for a period of ten seconds.
Astronomers have known for a long time that when compared to stars like our Sun, M-type stars are variable and unstable. While they are the smallest, coolest, and dimmest stars in our Universe, they tend to flare up at a far greater rate. In this case, the flare detected by the team was ten times larger than our Sun’s brightest flares at similar wavelengths.
Along with a smaller preceding flare, the entire event lasted fewer than two minutes of the 10 hours that ALMA was observing the star between January and March of last year. While it was already known that Proxima Centauri, like all M-type stars, experiences regular flare activity, this one appeared to be a rare event. However, stars like Proxima Centauri are also known to experienced regular, although smaller, X-ray flares.
All of this adds up to a bad case for habitability. As MacGregor explained in a recent NRAO press statement:
“It’s likely that Proxima b was blasted by high energy radiation during this flare. Over the billions of years since Proxima b formed, flares like this one could have evaporated any atmosphere or ocean and sterilized the surface, suggesting that habitability may involve more than just being the right distance from the host star to have liquid water.”
MacGregor and her colleagues also considered the possibility that Proxima Centauri is circled by several disks of dust. This was suggested by a previous study (also based on ALMA data) that indicated that the light output of both the star and flare together pointed towards the existence of debris belts around the star. However, after examining the ALMA data as a function of observing time, they were able to eliminate this as a possibility.
As Alycia J. Weinberger, also a researcher with the Carnegie Institution for Science and a co-author on the paper, explained:
“There is now no reason to think that there is a substantial amount of dust around Proxima Cen. Nor is there any information yet that indicates the star has a rich planetary system like ours.”
To date, studies that have looked at possible conditions on Proxima b have come to different conclusions as to whether or not it could retain an atmosphere or liquid water on its surface. While some have found room for “transient habitability” or evidence of liquid water, others have expressed doubt based on the long-term effects that radiation and flares from its star would have on a tidally-locked planet.
In the future, the deployment of next-generation instruments like the James Webb Space Telescope are expected to provide more detailed information on this system. With precise measurements of this star and its planet, the question of whether or not life can (and does) exist in this system may finally be answered.
And be sure to enjoy this animation of Proxima Centauri in motion, courtesy of NRAO outreach:
At a distance of 4.37 light-years from Earth, Alpha Centauri is the nearest star system to our own. For generations, scientists and speculative thinkers have pondered whether it might have a planetary system like our own Sun, and whether or not life may also exist there. Unfortunately, recent efforts to locate extra-solar planets in this star system have failed, with potential detections later shown to be the result of artifacts in the data.
In response to these failed efforts, several more ambitious projects are being developed to find exoplanets around Alpha Centauri. These include direct-imaging space telescopes like Project Blue and the interstellar mission known as Breakthrough Starshot. But according to a new study led by researchers from Yale University, existing data can be used to determine the probability of planets in this system (and even which kind).
The study which detailed their findings recently appeared in The Astronomical Journal under the title “Planet Detectability in the Alpha Centauri System“. The study was led by Lily Zhao, a graduate student from Yale University and a fellow with the National Science Foundation (NSF), and was co-authored by Debora Fischer, John Brewer and Matt Giguere of Yale and Bárbara Rojas-Ayala of the Universidad Andrés Bello in Chile.
For the sake of their study, Zhao and her team considered why efforts to locate planets within the the closest star system to our own have so far failed. This is surprising when one considers how, statistically speaking, Alpha Centauri is very likely to have a system if its own. As Prof. Fischer indicated in a recent Yale News press release:
“The universe has told us the most common types of planets are small planets, and our study shows these are exactly the ones that are most likely to be orbiting Alpha Centauri A and B… Because Alpha Centauri is so close, it is our first stop outside our solar system. There’s almost certain to be small, rocky planets around Alpha Centauri A and B.”
In addition to being a professor of astronomy at Yale University, Debora Fischer is also one of the leaders of the Yale Exoplanets Group. As an expert in her field, Fischer has devoted decades of her life to researching exoplanets and searching for Earth analogues beyond our Solar System. With partial funding provided by NASA and the National Science Foundation, the team relied on existing data collected by some of the latest exoplanet-hunting instruments.
These included CHIRON, a spectrograph mounted on the Small and Moderate Aperture Research Telescope System (SMARTS) at the Cerro Telolo Inter-American Observatory (CTIO) in Chile. This instrument was built by Fischer’s team, and the data it provided was combined with the High Accuracy Radial velocity Planet Searcher (HARPS) and the Ultraviolet and Visual Echelle Spectrograph (UVES) instruments on the ESO’s Very Large Telescope (VLT).
Using ten years of data collected by these instruments, Zhao and her colleagues then set up a grid system for the Alpha Centauri system. Rather than looking for signs of planets that did exist, they used the data to rule out what types of planets could not exist there. As Zhao told Universe Today via email:
“This study was special in that it used existing data of the Alpha Centauri system not to find planets, but to characterize what planets could not exist. By doing so, it returned more information about the system as a whole and provides guidance for future observations of this uniquely charismatic system.
In addition, the team analyzed the chemical composition of the stars in the Alpha Centauri system to learn more about the kinds of material that would be available to form planets. Based on the different values obtained by observations campaigns conducted by different telescopes on Alpha Centauri’s three stars (Alpha, Beta and Proxima), they were able to place constraints on what kinds of planets could exist there.
“We found that existing data rules out planets in the habitable zone above 53 Earth masses for alpha Centauri A, 8.4 Earth masses for Alpha Centauri B, and 0.47 Earth masses for Proxima Centauri,” said Zhao. “As for the chemical compositions, we found that the ratios of Carbon/Oxygen and Magnesium/Silicon for Alpha Centauri A and B are quite similar to that of the Sun.”
Basically, the results of their study effectively ruled out the possibility of any Jupiter-sized gas giants in the Alpha Centauri system. For Alpha Centauri A, they further found that planets that were less than 50 Earth masses could exist, while Alpha Centauri B might have planets smaller than 8 Earth masses. For Proxima Centauri, which we know to have at least one Earth-like planet, they determined that there might more that are less than half of Earth’s mass.
In addition to offering hope for exoplanet-hunters, this study carries with it some rather interesting implications for planetary habitability. Basically, the presence of rocky planets in the system is encouraging; but with no gas giants, a key ingredient in ensuring that planets remain habitable could be missing.
“[N]ot only could there still be habitable, Earth-mass planets around our closest stellar neighbors, but there also aren’t any gas giants that could endanger the survival of these potentially habitable, rocky planets,” said Zhao. “Furthermore, if these planets do exist, they are likely to have similar compositions to our very own Earth given the similarity in Alpha Cen A/B and our beloved Sun.”
At present, there are no instruments that have been able to confirm the existence of any exoplanets in Alpha Centauri. But as Zhao indicated, her and her teammates are optimistic that future surveys will have the necessary sensitivity to do it:
“[T]his very month has seen the commissioning of several next-generation instruments promising the precision necessary to discover these possible planets in the near future, and this analysis has shown that it is for sure worth it to keep looking!”
These include the ESO-built Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO) – which was recently installed at the Paranal Observatory – and the EXtreme PREcision Spectrometer (EXPRES) built at Yale University. This latter instrument is currently conducting an observation run at the Lowell Observatory in Arizona, which Zhao is participating in.
“These instruments are promising a precision of down to 10-30 cm/s and should be able to detect many more smaller, and further away planets – such as habitable planets around the Centauri stars,” said Zhao. “The field of view of these two instruments are slightly different (ESPRESSO has the southern hemisphere, where Alpha Centauri is, while EXPRES covers the northern hemisphere, for instance where the Kepler and many of the K2 fields are).”
With new instruments at their disposal, and methods like the one Zhao and her team developed, the closest star system to Earth is sure to become a veritable treasure trove for astronomers and exoplanet-hunters in the coming years. And anything we find there will surely become targets for direct studies by groups like Project Blue and Breakthrough Starshot. If ET resides next door, we’re sure to hear about it soon!
Proxima Centauri, in addition to being the closest star system to our own, is also the home of the closest exoplanet to Earth. The existence of this planet, Proxima b, was first announced in August of 2016 and then confirmed later that month. The news was met with a great deal of excitement, and a fair of skepticism, as numerous studies followed t were dedicated to determining if this planet could in fact be habitable.
Another important question has been whether or not Proxima Centauri could have any more objects orbiting it. According to a recent study by an international team of astronomers, Proxima Centauri is also home to a belt of cold dust and debris that is similar to the Main Asteroid Belt and Kuiper Belt in our Solar System. The existence of this dusty belt could indicate the presence of more planets in this star system.
The study, titled “ALMA Discovery of Dust Belts Around Proxima Centauri“, recently appeared online and is scheduled to appear in the Monthly Notices of the Astronomical Society. The study was led by Guillem Anglada from the Astrophysical Institute of Andalusia (CSIS), and included members from the Institute of Space Sciences (IEEC), the European Southern Observatory (ESO), the Joint ALMA Observatory, and multiple universities.
For their study, the team relied on data obtained by the Atacama Large Millimeter/submillimter Array (ALMA) at the ALMA Observatory in Chile. These observations revealed the glow of a cold dust belt that is roughly 1 to 4 AUs from Proxima Centauri – one to four times the distance between the Earth and the Sun. This puts it significantly further out than Proxima b, which orbits its sun at a distance of 0.0485 AU (~5% of Earth’s distance from the Sun).
Dust belts are essentially the leftover material that did not form into larger bodies withing a star system. The particles of rock and ice in these belts vary in size from being smaller than a millimeter across to asteroids that are many kilometers in diameter. Based on their observations, the team estimated that the belt in Proxima Centauri has a total mass that is about one-hundredth the mass of Earth.
The team also estimated that this belt experiences temperatures of about 43 K (-230°C; -382 °F), making it as cold as the Kuiper Belt. As Dr. Anglada explained the significance of these findings in a recent ESO press release:
“The dust around Proxima is important because, following the discovery of the terrestrial planet Proxima b, it’s the first indication of the presence of an elaborate planetary system, and not just a single planet, around the star closest to our Sun.”
The ALMA data also provided indications that Proxima Centauri might also have another belt located about ten times further out. In other words, Proxima Centauri may have two belts, just like our Solar System. If confirmed, this could indicate that this neighboring star also has a system of planets that fall within and between belts of unconsolidated material, which in turn is leftover from the early days of planet formation. As Dr. Anglada explained:
“This result suggests that Proxima Centauri may have a multiple planet system with a rich history of interactions that resulted in the formation of a dust belt. Further study may also provide information that might point to the locations of as yet unidentified additional planets.”
The very cold environment of this outer belt could also have some interesting implications, since its parent star is much dimmer than our own. Pedro Amado, who also hails from the Astrophysical Institute of Andalusia, was similarly enthusiastic about these findings. As he indicated, they are just the beginning of what is sure to be a long process of discovery about this system.
“These first results show that ALMA can detect dust structures orbiting around Proxima,” he said. “Further observations will give us a more detailed picture of Proxima’s planetary system. In combination with the study of protoplanetary discs around young stars, many of the details of the processes that led to the formation of the Earth and the Solar System about 4600 million years ago will be unveiled. What we are seeing now is just the appetiser compared to what is coming!”
This study is also likely to be of interest to those planning on conducting direct observations of the Alpha Centauri system, such as Project Blue. In the coming years, they hope to deploy a space telescope that will observe Alpha Centauri directly to study any exoplanets it may have. With a slight adjustment, this telescope could also take a gander at Proxima Centauri and aid in the hunt for a system of planets there.
And then there’s Breakthrough Starshot, the first proposed interstellar voyage which hopes to send a laser sail-driven nanocraft to Alpha Centauri in the coming decades. Recently, the scientists behind Starshot discussed the possibility of extending the mission to include a stopover in Proxima Centauri. Before such a mission can take place, the planners need to know what kind of dusty environment awaits it.
And of course, future studies will benefit from the deployment of next-generation instruments, like the James Webb Space Telescope (scheduled for launch in 2019) and the ESO’s Extremely Large Telescope (ELT) – which is expected to collect its first light in 2024.
We’ve spent a few articles on Universe Today talking about just how difficult it’s going to be to travel to other stars. Sending tiny unmanned probes across the vast gulfs between stars is still mostly science fiction. But to send humans on that journey? That’s just a level of technology beyond comprehension.
For example, the nearest star is Proxima Centauri, located a mere 4.25 light years away. Just for comparison, the Voyager spacecraft, the most distant human objects ever built by humans, would need about 50,000 years to make that journey.
I don’t know about you, but I don’t anticipate living 50,000 years. No, we’re going to want to make the journey more quickly. But the problem, of course, is that going more quickly requires more energy, new forms of propulsion we’ve only starting to dream up. And if you go too quickly, mere grains of dust floating through space become incredibly dangerous.
Based on our current technology, it’s more likely that we’re going to have to take our time getting to another star.
And if you’re going to go the slower route, you’ve got a couple of options. Create a generational ship, so that successive generations of humans are born, live out their lives, and then die during the hundreds or even thousands of year long journey to another star.
Imagine you’re one of the people destined to live and die, never reaching your destination. Especially when you look out your window and watch a warp ship zip past with all those happy tourists headed to Proxima Centauri, who were start enough to wait for warp drives to be invented.
No, you want to sleep for the journey to the nearest star, so that when you get there, it’s like no time passed. And even if warp drive did get invented while you were asleep, you didn’t have to see their smug tourist faces as they zipped past.
Is human hibernation possible? Can we do it long enough to survive a long-duration spaceflight journey and wake up again on the other side?
Before I get into this, we’re just going to have to assume that we never merge with our robot overlords, upload ourselves into the singularity, and effortlessly travel through space with our cybernetic bodies.
For some reason, that whole singularity thing never worked out, or the robots went on strike and refused to do our space exploration for us any more. And so, the job of space travel fell to us, the fragile, 80-year lifespanned mammals. Exploring the worlds within the Solar System and out to other stars, spreading humanity into the cosmos.
Come on, we know it’ll totally be the robots. But that’s not what the science fiction tells us, so let’s dig into it.
We see animals, and especially mammals hibernating all the time in nature. In order to be able survive over a harsh winter, animals are capable of slowing their heart rate down to just a few beats a minute. They don’t need to eat or drink, surviving on their fat stores for months at a time until food returns.
It’s not just bears and rodents that can do it, by the way, there are actually a couple of primates, including the fat-tailed dwarf lemur from Madagascar. That’s not too far away on the old family tree, so there might be hope for human hibernation after all.
In fact, medicine is already playing around with human hibernation to improve people’s chances to survive heart attacks and strokes. The current state of this technology is really promising.
They use a technique called therapeutic hypothermia, which lowers the temperature of a person by a few degrees. They can use ice packs or coolers, and doctors have even tried pumping a cooled saline solution through the circulatory system. With the lowered temperature, a human’s metabolism decreases and they fall unconscious into a torpor.
But the trick is to not make them so unconscious that they die. It’s a fine line.
The results have been pretty amazing. People have been kept in this torpor state for up to 14 days, going through multiple cycles.
The therapeutic use of this torpor is still under research, and doctors are learning if it’s helpful for people with heart attacks, strokes or even the progression of diseases like cancer. They’re also trying to figure out if there are any downsides, but so far, there don’t seem to be any long-term problems with putting someone in this torpor state.
A few years ago, SpaceWorks Enterprises delivered a report to NASA on how they could use this therapeutic hypothermia for long duration spaceflight within the Solar System.
Currently, a trip to Mars takes about 6-9 months. And during that time, the human passengers are going to be using up precious air, water and food. But in this torpor state, SpaceWorks estimates that the crew will a reduction in their metabolic rate of 50 to 70%. Less metabolism, less resources needed. Less cargo that needs to be sent to Mars.
The astronauts wouldn’t need to move around, so you could keep them nice and snug in little pods for the journey. And they wouldn’t get into fights with each other, after 6-9 months of nothing but day after day of spaceflight.
We know that weightlessness has a negative effect on the body, like loss of bone mass and atrophy of muscles. Normally astronauts exercise for hours every day to counteract the negative effects of the reduced gravity. But SpaceWorks thinks it would be more effective to just put the astronauts into a rotating module and let artificial gravity do the work of maintaining their conditioning.
They envision a module that’s 4 metres high and 8 metres wide. If you spin the habitat at 20 revolutions per minute, you give the crew the equivalent of Earth gravity. Go at only 11.8 RPM and it’ll feel like Mars gravity. Down to 7.8 and it’s lunar gravity.
Normally spinning that fast in a habitat that small would be extremely uncomfortable as the crew would experience different forces at different parts of their body. But remember, they’ll be in a state of torpor, so they really won’t care.
Current plans for sending colonists to Mars would require 40 ton habitats to support 6 people on the trip. But according to SpaceWorks, you could reduce the weight down to 15 tons if you just let them sleep their way through the journey. And the savings get even better with more astronauts.
The crew probably wouldn’t all sleep for the entire journey. Instead, they’d sleep in shifts for a few weeks. Taking turns to wake up, check on the status of the spacecraft and crew before returning to their cryosleep caskets.
What’s the status of this now? NASA funded stage 1 of the SpaceWorks proposal, and in July, 2016 NASA moved forward with Phase 2 of the project, which will further investigate this technique for Mars missions, and how it could be used even farther out in the Solar System.
Elon Musk should be interested in seeing their designs for a 100-person module for sending colonists to Mars.
In addition, the European Space Agency has also been investigating human hibernation, and a possible way to enable long-duration spaceflight. They have plans to test out the technology on various non-hibernating mammals, like pigs. If their results are positive, we might see the Europeans pushing this technology forward.
Can we go further, putting people to sleep for decades and maybe even the centuries it would take to travel between the stars?
Right now, the answer is no. We don’t have any technology at our disposal that could do this. We know that microbial life can be frozen for hundreds of years. Right now there are parts of Siberia unfreezing after centuries of permafrost, awakening ancient microbes, viruses, plants and even animals. But nothing on the scale of human beings.
When humans freeze, ice crystals form in our cells, rupturing them permanently. There is one line of research that offers some hope: cryogenics. This process replaces the fluids of the human body with an antifreeze agent which doesn’t form the same destructive crystals.
Scientists have successfully frozen and then unfrozen 50-milliliters (almost a quarter cup) of tissue without any damage.
In the next few years, we’ll probably see this technology expanded to preserving organs for transplant, and eventually entire bodies, and maybe even humans. Then this science fiction idea might actually turn into reality. We’ll finally be able to sleep our way between the stars.
In April of 2016, Russian billionaire Yuri Milner announced the creation of Breakthrough Starshot. As part of his non-profit scientific organization (known as Breakthrough Initiatives), the purpose of Starshot was to design a lightsail nanocraft that would be capable of reaching the nearest star system – Alpha Centauri (aka. Rigel Kentaurus) – within our lifetime.
Since its inception, the scientists and engineers behind the Starshot concept have sought to address the challenges that such a mission would face. Similarly, there have been many in the scientific community who have also made suggestions as to how such a concept could work. The latest comes from the Max Planck Institute for Solar System Research, where two researchers came up with a novel way of slowing the craft down once it reaches its destination.
To recap, the Starshot concept involves a small, gram-scale nanocraft being towed by a lightsail. Using a ground-based laser array, this lightsail would be accelerated to a velocity of about 60,000 km/s (37,282 mps) – or 20% the speed of light. At this speed, the nanocraft would be able to reach the closest star system to our own – Alpha Centauri, located 4.37 light-years away – in just 20 years time.
Naturally, this presents a number of technical challenges – which include the possibility of a collision with interstellar dust, the proper shape of the lightsail, and the sheer energy requirements for powering the laser array. But equally important is the idea of how such a craft would slow down once it reached its destination. With no lasers at the other end to apply breaking energy, how would the craft slow down enough to begin studying the system?
It was this very question that René Heller and Michael Hippke chose to address in their study, “Deceleration of high-velocity interstellar photon sails into bound orbits at Alpha Centauri“. Heller is an astrophysicts who is currently assisting the ESA with its preparations for the upcoming PLAnetary Transits and Oscillations of stars (PLATO) mission – an exoplanet hunter being deployed as part of their Cosmic Vision program.
With the help IT specialist Michael Hippke, the two considered what would be needed for interstellar mission to reach Alpha Centauri, and provide good scientific returns upon its arrival. This would require that braking maneuvers be conducted once it arrived so the the spacecraft would not overshoot the system in the blink of an eye. As they state in their study:
“Although such an interstellar probe could reach Proxima 20 years after launch, without propellant to slow it down it would traverse the system within hours. Here we demonstrate how the stellar photon pressures of the stellar triple Alpha Cen A, B, and C (Proxima) can be used together with gravity assists to decelerate incoming solar sails from Earth.”
For the sake of their calculations, Heller and Hippke estimated that the craft would weigh less than 100 grams (3.5 ounces), and would be mounted on a sail measuring 100,000 m² (1,076,391 square foot) in surface area. Once these were complete, Hippke adapted them into a series of computer simulations. Based on their results, they proposed an entirely new mission concept that do away with the need for lasers entirely.
In essence, their revised concept called for an Autonomous Active Sail (AAS) craft that would provide for its own propulsion and stopping power. This craft would deploy its sail while in the Solar System and use the Sun’s solar wind to accelerate it to high speeds. Once it reached the Alpha Centauri System, it would redeploy its sail so that incoming radiation from Alpha Centauri A and B would have the effect of slowing it down.
An added bonus of this proposed maneuver is that the craft, once it had been decelerated to the point that it could effectively explore the Alpha Centauri system, could then use a gravity assist from these stars to reroute itself towards Proxima Centauri. Once there, it could conduct the first up-close exploration of Proxima b – the closest exoplanet to Earth – and determine what its atmospheric and surface conditions are like.
Since the existence of this planet was first announced by the European Southern Observatory back in August of 2016, there has been much speculation about whether or not it could be habitable. Having a mission that could examine it to check for the telltale markers – a viable atmosphere, a magnetosphere, and liquid water on the surface – would surely settle that debate.
As Heller explained in a press release from the Max Planck Institute, this concept presents quite a few advantages, but comes with its share of trade offs – not the least of which is the time it would take to get to Alpha Centauri. “Our new mission concept could yield a high scientific return, but only the grandchildren of our grandchildren would receive it,” he said. “Starshot, on the other hand, works on a timescale of decades and could be realized in one generation. So we might have identified a longterm, follow-up concept for Starshot.”
At present, Heller and Hippke are discussing their concept with Breakthrough Starshot to see if it would be viable. One individual who has looked over their work is Professor Avi Loeb, the Frank B. Baird Jr. Professor of Science at Harvard University, and the chairman of the Breakthrough Foundation’s Advisory Board. As he told Universe Today via email, the concept put forth by Heller and Hippke is worthy of consideration, but has its limitations:
“If it is possible to slow down a spacecraft by starlight (and gravitational assist), then it is also possible to launch it in the first place by the same forces… If so, why is the recently announced Breakthrough Starshot project using a laser and not Sunlight to propel our spacecraft? The answer is that our envisioned laser array can push the sail with an energy flux that is a million times larger than the local solar flux.
“In using starlight to reach relativistic speeds, one must use an extremely thin sail. In the new paper, Heller and Hippke consider the example of a milligram instead of a gram-scale sail. For a sail of area ten square meters (as envisioned in our Starshot concept study), the thickness of their sail must be only a few atoms. Such a surface is orders of magnitude thinner than the wavelength of light that it aims to reflect, and so its reflectivity would be low. It does not appear feasible to reduce the weight by so many orders of magnitude and yet maintain the rigidity and reflectivity of the sail material.
“The main constraint in defining the Starshot concept was to visit Alpha Centauri within our lifetime. Extending the travel time beyond the lifetime of a human, as advocated in this paper, would make it less appealing to the people involved. Also, one should keep in mind that the sail must be accompanied by electronics which will add significantly to its weight.”
In short, if time is not a factor, we can envision that our first attempts to reach another Solar System may indeed involve an AAS being propelled and slowed down by solar wind. But if we’re willing to wait centuries for such a mission to be completed, we might also consider sending rockets with conventional engines (possibly even crewed ones) to Alpha Centauri.
But if we are intent on getting there within our own lifetimes, then a laser-driven sail or something similar will have be the way to go. Humanity has spent over half a century exploring what’s in our own backyard, and some of us are impatient to see what’s next door!