Astronomers have found plenty of white dwarf stars surrounded by debris disks. Those disks are the remains of planets destroyed by the star as it evolved. But they’ve found one intact Jupiter-mass planet orbiting a white dwarf.
Are there more white dwarf planets? Can terrestrial, Earth-like planets exist around white dwarfs?
Despite the fact that we’ve discovered thousands of them, exoplanets are hard to find. And some types are harder to find than others. Naturally, some of the hardest ones to find are the ones we most want to find. What can we do?
Keep working on it, and that’s what a trio of Chinese scientists are doing.
Proxima b, the closest exoplanet to our Solar System, has been a focal point of scientific study since it was first confirmed (in 2016). This terrestrial planet (aka. rocky) orbits Proxima Centauri, an M-type (red dwarf) star located 4.2 light-years beyond our Solar System – and is a part of the Alpha Centauri system. In addition to its proximity and rocky composition, it is also located within its parent star’s habitable zone (HZ).
Until a mission can be sent to this planet (such as Breakthrough Starshot), astrobiologists are forced to postulate about the possibility that life could exist there. Unfortunately, an international campaign that monitored Proxima Centauri for months using nine space- and ground-based telescopes recently spotted an extreme flare coming from the star, one which would have rendered Proxima b uninhabitable.
In recent decades, over 4,000 extrasolar planets have been confirmed beyond our Solar System. With so many planets available for study, astronomers have learned a great deal about the types of planets that exist out there and what kind of conditions are prevalent. For instance, they have been able to get a better idea of just how common habitable planets are (at least by our standards).
As it turns out, a surprisingly high number of planets out there could support life. That is the conclusion reached by a team of astronomers and planetary scientists who conducted a study of the possible sizes of habitable zones (HZ) based on stellar classification. After considering many planets could stably orbit within them, they came to the conclusion that stars with no Jupiter-sized gas giants can have as many as seven habitable planets!
In 2017, an international team of astronomers announced a momentous discovery. Based on years of observations, they found that the TRAPPIST-1 system (an M-type red dwarf located 40 light-years from Earth) contained no less than seven rocky planets! Equally exciting was the fact that three of these planets were found within the star’s Habitable Zone (HZ), and that the system itself has had 8 billion years to develop the chemistry for life.
At the same time, the fact that these planets orbit tightly around a red dwarf star has given rise to doubts that these three planets could maintain an atmosphere or liquid water for very long. According to new research by an international team of astronomers, it all comes down to the composition of the debris disk that the planets formed from and whether or not comets were around to distribute water afterward.
Since the Kepler Space Telescope was launched into space, the number of known planets beyond our Solar System (exoplanets) has grown exponentially. At present, 3,917 planets have been confirmed in 2,918 star systems, while 3,368 await confirmation. Of these, about 50 orbit within their star’s circumstellar habitable zone (aka. “Goldilocks Zone”) , the distance at which liquid water can exist on a planets’ surface.
However, recent research has raised the possibility that we consider to be a habitable zone is too optimistic. According to a new study that recently appeared online, titled “A Limited Habitable Zone for Complex Life“, habitable zones could be much narrower than originally thought. These finds could have a drastic impact on the number of planets scientists consider to be “potentially habitable”.
NASA’s rover Curiosity said ‘Goodbye Kimberley’ having fulfilled her objectives of drilling into a cold red sandstone slab, sampling the tantalizing grey colored interior and pelting the fresh bore hole with a pinpoint series of parting laser blasts before seeking new adventures on the road ahead towards the inviting slopes of Mount Sharp, her ultimate destination.
Curiosity successfully drilled her 3rd hole deep into the ‘Windjama’ rock target at the base of Mount Remarkable and within the science waypoint at a region called “The Kimberley” on May 5, Sol 621.
Since then, the 1 ton robot carefully scrutinized the resulting 2.6 inches (6.5 centimeters) deep bore hole and the mound of dark grey colored drill tailings piled around for an up close examination of the texture and composition with the MAHLI camera and spectrometers at the end of her 7-foot-long (2 meters) arm to glean every last drop of science before moving on.
Multiple scars clearly visible inside the drill hole and on the Martian surface resulting from the million watt laser firings of the Mast mounted Chemistry and Camera (ChemCam) instrument left no doubt of Curiosity’s capabilities or intentions.
Furthermore she successfully delivered pulverized and sieved samples to the pair of onboard miniaturized chemistry labs; the Chemistry and Mineralogy instrument (CheMin) and the Sample Analysis at Mars instrument (SAM) – for chemical and compositional analysis.
Curiosity completed an “intensive investigation of ‘The Kimberley’, having successfully drilled, acquired and dropped samples into CheMin and SAM,” wrote science team member Ken Herkenhoff in an update.
“MAHLI has taken lots of excellent images of the drill hole, including some during the night with LEDs on, nicely showing the ChemCam LIBS spots.”
“The initial analysis of this new sample by Chemin is ongoing, requiring repeated overnight integration to build up high-quality data,” says Herkenhoff.
The rover’s earth bound handlers also decided that one drill campaign into Kimberley was enough.
So the rover will not be drilling into any other rock targets here.
And it may be a very long time before the next drilling since the guiding team of scientists and engineers wants desperately to get on and arrive at the foothills of Mount Sharp as soon as possible.
But the robot will undoubtedly be busy with further analysis of the ‘Windjana’ sample along the way, since there’s plenty of leftover sample material stored in the CHIMRA sample processing mechanism to allow future delivery of samples when the rover periodically pauses during driving.
“Windjana” is named after a gorge in Western Australia.
It’s been a full year since the first two drill campaigns were conducted during 2013 at the ‘John Klein’ and ‘Cumberland’ outcrop targets inside Yellowknife Bay. They were both mudstone rock outcrops and the interiors were markedly different in color.
“The drill tailings from this rock are darker-toned and less red than we saw at the two previous drill sites,” said Jim Bell of Arizona State University, Tempe, deputy principal investigator for Curiosity’s Mast Camera (Mastcam).
“This suggests that the detailed chemical and mineral analysis that will be coming from Curiosity’s other instruments could reveal different materials than we’ve seen before. We can’t wait to find out!”
The science team chose Windjana for drilling “to analyze the cementing material that holds together sand-size grains in this sandstone,” says NASA.
“The Kimberley Waypoint was selected because it has interesting, complex stratigraphy,” Curiosity Principal Investigator John Grotzinger, of the California Institute of Technology, Pasadena, told me.
Curiosity departed the ancient lakebed at the Yellowknife Bay region in July 2013 where she discovered a habitable zone with the key chemical elements and a chemical energy source that could have supported microbial life billions of years ago – and thereby accomplished the primary goal of the mission.
Windjama lies some 2.5 miles (4 kilometers) southwest of Yellowknife Bay.
Curiosity still has about another 4 kilometers to go to reach the foothills of Mount Sharp sometime later this year.
The sedimentary layers of Mount Sharp, which reaches 3.4 miles (5.5 km) into the Martian sky, is the six wheeled robots ultimate destination inside Gale Crater because it holds caches of water altered minerals. Such minerals could possibly indicate locations that sustained potential Martian life forms, past or present, if they ever existed.
Stay tuned here for Ken’s continuing Curiosity, Opportunity, Orion, SpaceX, Boeing, Orbital Sciences, LADEE, MAVEN, MOM, Mars and more planetary and human spaceflight news.
Curiosity maneuvers into ‘Kimbeley’ and scans scientifically intriguing Martian rock outcrops in search of next drilling location exhibiting several shallow hills in foreground and dramatic Gale crater rim backdrop. Rover tracks at right in this colorized Navcam photomosaic assembled from raw images snapped on Sol 589, April 3, 2014.
Credit: NASA/JPL/Marco Di Lorenzo /Ken Kremer – kenkremer.com[/caption]
NASA’s car sized Curiosity rover has arrived at a scientifically enticing science destination at “The Kimberley Waypoint” where researchers hope to carry out the next drilling operation into alien Martian terrain in search of further clues about ancient Red Planet environments that may have been favorable for life.
“We are officially in ‘The Kimberley’ now,” Curiosity Principal Investigator John Grotzinger, of the California Institute of Technology, Pasadena, told Universe Today.
Since arriving in the Kimberley region, Curiosity’s earth-bound handlers have been maneuvering the 1 ton robot to thoroughly survey the destination dubbed “The Kimberley”.
Why was Kimberley chosen as a science destination?
“The Kimberley” has interesting, complex stratigraphy,” Grotzinger told me.
The team moved the six wheeled robot further this week in search of a suitable location to conduct the next drilling operation. The terrain is replete with diverse rock types and extensive outcrops.
I asked Grotzinger if today’s (April 5) location at ‘The Kimberley’ is the intended drill site?
“It’s a possible drill site,” Grotzinger replied.
“Pending further evaluation,” he noted.
Curiosity drove the final stretch of some 98 feet (30 meters) on Wednesday, April 2, required to arrive at a major stopping waypoint planned since early 2013 for up close study of the Red Planet’s rocks.
Along the recent dune filled path to ‘The Kimberley’, Curiosity snapped breathtaking landscapes around the irresistible ‘Junda’ outcrop, much like a tourist.
See our photomosaics showing the spectacularly inviting terrain around Kimberly and Junda, above and below, by Marco Di Lorenzo and Ken Kremer.
The state-of-the-art robot now sits at a vantage point at “The Kimberley” enabling a detailed photographic survey of the rock exposures and surroundings with the high resolution Mastcam cameras.
The new imagery will be used to select the most scientifically productive drilling locations.
“It is named after a remote region of western Australia,” Grotzinger informed me.
The team chose Kimberley because its lies at the intersection of four different types of rocks, including striated rocks overlain by others and deposited in a decipherable geological relationship to each other.
Researchers directed Curiosity on a pinpoint drive to ‘Kimberley’ after high resolution imagery and mineral mapping spectrometry gathered by NASA’s powerful telescopic cameras aboard the Mars Reconnaissance Orbiter (MRO) circling overhead piqued their interest.
“This is the spot on the map we’ve been headed for, on a little rise that gives us a great view for context imaging of the outcrops at the Kimberley,” said Melissa Rice, Curiosity science planning lead, of Caltech.
The team expects Curiosity to investigate Kimberley for several weeks of observations, including sample-drilling and onboard laboratory analysis of the area’s rocks with the CheMin and SAM miniaturized chemistry labs.
If drilling is warranted, Kimberley would be the site of Curiosity’s first drilling operation since boring into the ‘John Klein’ and ‘Cumberland’ outcrop targets during the spring of 2013 at Yellowknife Bay.
The robot has conducted cleaning activities of SAM, CheMin and the CHIMRA sample handling mechanism in anticipation of boring into the Martian outcrops and delivering powdery, pulverized samples of cored Martian rocks to SAM and CheMin – waiting patiently inside the robots belly to eat something exciting from the Red Planet.
Curiosity departed the Yellowknife Bay region in July 2013 where she discovered a habitable zone and thereby accomplished the primary goal of the mission.
To date, Curiosity’s odometer totals 3.8 miles (6.1 kilometers) since landing inside Gale Crater on Mars in August 2012. She has taken over 137,000 images.
The sedimentary foothills of Mount Sharp, which reaches 3.4 miles (5.5 km) into the Martian sky, is the 1 ton robots ultimate destination inside Gale Crater because it holds caches of water altered minerals. Such minerals could possibly indicate locations that sustained potential Martian life forms, past or present, if they ever existed.
Curiosity has some 4 kilometers to go to reach the base of Mount Sharp.
She may arrive at the lower reaches of Mount Sharp sometime in the latter half of 2014, but must first pass through a potentially treacherous dune field.
It’s a given. It won’t be long until human technology will expand our repertoire of cataloged exoplanets to astronomical levels. Of these, a huge number will be considered within the “habitable zone”. However, isn’t it a bit egotistical of mankind to assume that life should be “as we know it”? Now astrobiologists/scientists like Dirk Schulze-Makuch with the Washington State University School of Earth and Environmental Sciences and Abel Mendez from the University of Puerto Rico at Aricebo are suggesting we take a less limited point of view.
“In the next few years, the number of catalogued exoplanets will be counted in the thousands. This will vastly expand the number of potentially habitable worlds and lead to a systematic assessment of their astrobiological potential. Here, we suggest a two-tiered classification scheme of exoplanet habitability.” says Schulze-Makuch (et al). “The first tier consists of an Earth Similarity Index (ESI), which allows worlds to be screened with regard to their similarity to Earth, the only known inhabited planet at this time.”
Right now, an international science team representing NASA, SETI,the German Aerospace Center, and four universities are ready to propose two major questions dealing with our quest for life – both as we assume and and alternate. According to the WSU news release:
“The first question is whether Earth-like conditions can be found on other worlds, since we know empirically that those conditions could harbor life,” Schulze-Makuch said. “The second question is whether conditions exist on exoplanets that suggest the possibility of other forms of life, whether known to us or not.”
Within the next couple of weeks, Schulze-Makuch and his nine co-authors will publish a paper in the Astrobiology journal outlining their future plans for exoplanet classification. The double approach will consist of an Earth Similarity Index (ESI), which will place these newly found worlds within our known parameters – and a Planetary Habitability Index (PHI), that will account for more extreme conditions which could support surrogate subsistence.
“The ESI is based on data available or potentially available for most exoplanets such as mass, radius, and temperature.” explains the team. “For the second tier of the classification scheme we propose a Planetary Habitability Index (PHI) based on the presence of a stable substrate, available energy, appropriate chemistry, and the potential for holding a liquid solvent. The PHI has been designed to minimize the biased search for life as we know it and to take into account life that might exist under more exotic conditions.”
Assuming that life could only exist on Earth-like planets is simply narrow-minded thinking, and the team’s proposal and modeling efforts will allow them to judiciously filter new discoveries with speed and high level of probability. It will allow science to take a broader look at what’s out there – without being confined to assumptions.
“Habitability in a wider sense is not necessarily restricted to water as a solvent or to a planet circling a star,” the paper’s authors write. “For example, the hydrocarbon lakes on Titan could host a different form of life. Analog studies in hydrocarbon environments on Earth, in fact, clearly indicate that these environments are habitable in principle. Orphan planets wandering free of any central star could likewise conceivably feature conditions suitable for some form of life.”
Of course, the team admits an alien diversity is surely a questionable endeavor – but why risk the chance of discovery simply on the basis that it might not happen? Why put a choke-hold on creative thinking?
“Our proposed PHI is informed by chemical and physical parameters that are conducive to life in general,” they write. “It relies on factors that, in principle, could be detected at the distance of exoplanets from Earth, given currently planned future (space) instrumentation.”
Original News Source: WSU News. For Further Reading: A Two-Tiered Approach to Assessing the Habitability of Exoplanets.
It’s referred to as the “Goldilock’s Zone”, but this area in space isn’t meant for sleepy or hungry bears – it’s the relative area in which life can evolve and sustain. This habitable region has some fairly strict parameters, such as certain star types and rigid distance limits, but new research shows it could be considerably larger than estimated.
In a study done by Manoj Joshi and Robert Haberle, the team considered the relationship which occurs between the radiation for red dwarf stars and a possible planet’s reflective qualities. Known as albedo, this ability to “bounce back” light waves has a great deal to do with surface layers, such as ice and snow. Unlike our G-type Sun, the M-class red dwarf is much cooler and produces energy at longer wavelengths. This means a great deal of the radiation is absorbed – rather than reflected – turning the ice and snow into possible liquid water. And, as we know, water is considered to be a primary requirement for life.
“We knew that red dwarfs emit energy at a different wavelength, and we wanted to find out exactly what that might mean for the albedo of planets orbiting these stars.” explained Dr. Joshi from the National Centre for Atmospheric Science, who carried out the research in collaboration with Robert Haberle from the NASA Ames Research Centre.
What makes this theory even more charming is that M-class stars make up a very substantial portion of our galaxy’s total population – meaning there’s even more possible Goldilock’s Zones yet to be discovered. Considering the lifespan of a red dwarf star also increases the chances – as well as the distance a planet would need to be located for these properties to happen.
“M-stars comprise 80% of main-sequence stars, and so their planetary systems provide the best chance for finding habitable planets, i.e.: those with surface liquid water. We have modelled the broadband albedo or reflectivity of water ice and snow for simulated planetary surfaces orbiting two observed red dwarf stars (or M-stars) using spectrally resolved data of the Earth’s cryosphere.” explains Joshi. “In addition, planets with significant ice and snow cover will have significantly higher surface temperatures for a given stellar flux if the spectral variation of cryospheric albedo is considered, which in turn implies that the outer edge of the habitable zone around M-stars may be 10-30% further away from the parent star than previously thought.”
Have we discovered planets around red dwarf stars? The answer is yes. In order to calculate the effects of radiation and albedo, the team chose to use similar M-class stars, Gliese 436 and GJ 1214, and applied it to a simulated planet with an average surface temperature of 200 K. Why that particular temperature? In this circumstance, it’s the temperature at which one bar of carbon-dioxide condenses – a rough indicator of the outer edge of a habitable zone. It is theorized that anything registering below this temperature is too cold to harbor life.
What the team found was high albedo planets register a higher surface temperature when exposed to longer wavelength radiation. This means ice and snow covered planets could exist much further away from a red dwarf parent star – as much as one third more the distance.
“Previous studies haven’t included such detailed calculations of the different albedo effects of ice and snow.” explains Joshi. “But we were a little surprised how big the effect was.”