from the wait-didn't-he-die-on-November-15-1630? dept.
After nine years in deep space collecting data that indicate our sky to be filled with billions of hidden planets - more planets even than stars - NASA's Kepler space telescope has run out of fuel needed for further science operations. NASA has decided to retire the spacecraft within its current, safe orbit, away from Earth. Kepler leaves a legacy of more than 2,600 planet discoveries from outside our solar system, many of which could be promising places for life.
"As NASA's first planet-hunting mission, Kepler has wildly exceeded all our expectations and paved the way for our exploration and search for life in the solar system and beyond," said Thomas Zurbuchen, associate administrator of NASA's Science Mission Directorate in Washington. "Not only did it show us how many planets could be out there, it sparked an entirely new and robust field of research that has taken the science community by storm. Its discoveries have shed a new light on our place in the universe, and illuminated the tantalizing mysteries and possibilities among the stars."
Kepler has opened our eyes to the diversity of planets that exist in our galaxy. The most recent analysis of Kepler's discoveries concludes that 20 to 50 percent of the stars visible in the night sky are likely to have small, possibly rocky, planets similar in size to Earth, and located within the habitable zone of their parent stars. That means they're located at distances from their parent stars where liquid water - a vital ingredient to life as we know it - might pool on the planet surface.
[...] Before retiring the spacecraft, scientists pushed Kepler to its full potential, successfully completing multiple observation campaigns and downloading valuable science data even after initial warnings of low fuel. The latest data, from Campaign 19, will complement the data from NASA's newest planet hunter, the Transiting Exoplanet Survey Satellite, launched in April. TESS builds on Kepler's foundation with fresh batches of data in its search of planets orbiting some 200,000 of the brightest and nearest stars to the Earth, worlds that can later be explored for signs of life by missions such as NASA's James Webb Space Telescope.
The Dawn spacecraft orbiting Ceres will also exhaust the remainder of its hydrazine in the coming days. It will maintain an orbit around Ceres for decades, if not centuries.
NASA Kepler Telescope Discovers 715 New Planets
Kepler Proves it can Still Find Planets
74 Small Exoplanets With Circular Orbits Identified
NASA's Kepler Mission Discovers Earth-Like Planet In Sun-Like Star's Habitable Zone
Kepler Extended Mission Finds More Exoplanets
NASA's Kepler Mission Doubles Number of "Verified" Exoplanets, Including 9 Potentially Habitable
NASA Identifies "Pumpkin Stars"
Kepler Exoplanet Results Briefing on June 19th, Conference From 19th-23rd
Google Researchers Discover an 8th Planet in the Kepler-90 System
Citizen Scientists Credited for Discovery of Multi-Planet System
Kepler's K2 Mission Going Strong With Another 95 New Exoplanets Confirmed
Kepler Telescope Spots a Fast Supernova
NASA's TESS Mission Set to Launch on Wednesday, April 18
Researchers Suggest an Abundance of "Water World" Exoplanets
NASA's Dawn Spacecraft Nears the End of its Mission
New Evidence Supports Existence of Neptune-Sized Exomoon Orbiting Kepler-1625b
Gaia Observations Could Reduce the Number of Exoplanets Considered Potentially Habitable
"NASA's Kepler mission has doubled the number of known planets outside of our solar system. In what can only be described as a "bonanza", 715 new planets have been reported thanks to the Kepler space telescope's planet-hunting mission. Using a new method for verifying potential planets led to the volume of new discoveries from Kepler, which aims to help humans search for other worlds that may be like Earth."
Just over a year and a half ago, the Kepler space telescope suffered a failure of the second of its four stabilizing reaction wheels, prompting a 'shutdown' of its data–gathering mission because, if nothing else, the sun itself would continuously put pressure on the telescope to rotate. However, some engineers figured out that if they rotate Kepler to near-parallel to the sun, the solar pressure is evenly distributed across its surface and acts as kind of a third wheel.
Now, a team of scientists have announced Kepler is still helping us make discoveries. From the Harvard CfA:
Due to Kepler's reduced pointing capabilities, extracting useful data requires sophisticated computer analysis. Vanderburg and his colleagues developed specialized software to correct for spacecraft movements, achieving about half the photometric precision of the original Kepler mission.
Kepler's new life began with a 9-day test in February 2014. When Vanderburg and his colleagues analyzed that data, they found that Kepler had detected a single planetary transit.
The newfound planet, HIP 116454b, has a diameter of 20,000 miles, two and a half times the size of Earth. HARPS-N showed that it weighs almost 12 times as much as Earth. This makes HIP 116454b a super-Earth, a class of planets that doesn't exist in our solar system. The average density suggests that this planet is either a water world (composed of about three-fourths water and one-fourth rock) or a mini-Neptune with an extended, gaseous atmosphere.
Researchers from the Massachusetts Institute of Technology and Aarhus University have found that 74 small exoplanets orbit their stars in circular rather than eccentric patterns, suggesting that orbital regularity is common. The results could enhance the odds of finding Earth-sized exoplanets hospitable to life:
These 74 exoplanets, which orbit 28 stars, are about the size of Earth, and their circular trajectories stand in stark contrast to those of more massive exoplanets, some of which come extremely close to their stars before hurtling far out in highly eccentric, elongated orbits.
"Twenty years ago, we only knew about our solar system, and everything was circular and so everyone expected circular orbits everywhere," says Vincent Van Eylen, a visiting graduate student in MIT's Department of Physics. "Then we started finding giant exoplanets, and we found suddenly a whole range of eccentricities, so there was an open question about whether this would also hold for smaller planets. We find that for small planets, circular is probably the norm."
Ultimately, Van Eylen says that's good news in the search for life elsewhere. Among other requirements, for a planet to be habitable, it would have to be about the size of Earth — small and compact enough to be made of rock, not gas. If a small planet also maintained a circular orbit, it would be even more hospitable to life, as it would support a stable climate year-round. (In contrast, a planet with a more eccentric orbit might experience dramatic swings in climate as it orbited close in, then far out from its star.)
The team chose 28 stars with multiplanet systems that have been previously observed by the Kepler space observatory, and for which mass and radius had been determined using asteroseismology. Every one of the 74 known exoplanets orbiting those 28 stars were found to maintain circular orbits.
NASA has announced today the discovery of Kepler-452b, an Earth-like planet in a Sun-like star's habitable zone:
Kepler-452b is 60 percent larger in diameter than Earth and is considered a super-Earth-size planet. While its mass and composition are not yet determined, previous research suggests that planets the size of Kepler-452b have a good chance of being rocky.
While Kepler-452b is larger than Earth, its 385-day orbit is only 5 percent longer. The planet is 5 percent farther from its parent star Kepler-452 than Earth is from the Sun. Kepler-452 is 6 billion years old, 1.5 billion years older than our sun, has the same temperature, and is 20 percent brighter and has a diameter 10 percent larger.
The Kepler-452 system is located 1,400 light-years away in the constellation Cygnus.
Despite mechanical failures, the Kepler space observatory continues to find exoplanets in its extended K2 mission phase:
Between 2009 and 2013, Kepler became the most successful planet-hunting machine ever, discovering at least 1,030 planets and more than 4,600 possible others in a single patch of sky. When a mechanical failure stripped the spacecraft of its ability to point precisely among the stars, engineers reinvented it in 2014 as the K2 mission, which looks at different parts of the cosmos for shorter periods of time.
In its first year of observing, K2 has netted more than 100 confirmed exoplanets, says astronomer Ian Crossfield at the University of Arizona in Tucson. They include a surprising number of systems in which more than one planet orbits the same star. The K2 planets are also orbiting hotter stars than are many of the Kepler discoveries.
[...] The original Kepler mission was designed to answer a specific question: what fraction of Sun-like stars have Earth-size planets around them? Unbound by those constraints — even if not as good at pointing itself — K2 has been able to explore wider questions of planetary origin and evolution. "Now we get to look at a much bigger variety," says Steve Howell, the mission's project scientist at NASA's Ames Research Center in Moffett Field, California.
And because K2 looks at stars that are generally brighter and closer to Earth than Kepler did, the exoplanets that the mission finds are likely to be the best studied for the foreseeable future. This is because they are near enough to allow astronomers to explore them with other telescopes on Earth and in space.
NASA's Kepler mission has discovered a new batch of verified exoplanets, including nine that are potentially habitable:
NASA's Kepler mission has verified 1,284 new planets – the single largest finding of planets to date. "This announcement more than doubles the number of confirmed planets from Kepler," said Ellen Stofan, chief scientist at NASA Headquarters in Washington. "This gives us hope that somewhere out there, around a star much like ours, we can eventually discover another Earth."
Analysis was performed on the Kepler space telescope's July 2015 planet candidate catalog, which identified 4,302 potential planets. For 1,284 of the candidates, the probability of being a planet is greater than 99 percent – the minimum required to earn the status of "planet." An additional 1,327 candidates are more likely than not to be actual planets, but they do not meet the 99 percent threshold and will require additional study. The remaining 707 are more likely to be some other astrophysical phenomena. This analysis also validated 984 candidates previously verified by other techniques.
[...] In the newly-validated batch of planets, nearly 550 could be rocky planets like Earth, based on their size. Nine of these orbit in their sun's habitable zone, which is the distance from a star where orbiting planets can have surface temperatures that allow liquid water to pool. With the addition of these nine, 21 exoplanets now are known to be members of this exclusive group.
False Positive Probabilities For All Kepler Objects of Interest: 1284 Newly Validated Planets and 428 Likely False Positives (DOI: 10.3847/0004-637x/822/2/86)
NASA has found fast-spinning and orange "pumpkin stars" that appear to be the squashed result of ongoing binary mergers:
Astronomers using observations from NASA's Kepler and Swift missions have discovered a batch of rapidly spinning stars that produce X-rays at more than 100 times the peak levels ever seen from the sun. The stars, which spin so fast they've been squashed into pumpkin-like shapes, are thought to be the result of close binary systems where two sun-like stars merge. "These 18 stars rotate in just a few days on average, while the sun takes nearly a month," said Steve Howell, a senior research scientist at NASA's Ames Research Center in Moffett Field, California, and leader of the team. "The rapid rotation amplifies the same kind of activity we see on the sun, such as sunspots and solar flares, and essentially sends it into overdrive."
The most extreme member of the group, a K-type orange giant dubbed KSw 71, is more than 10 times larger than the sun, rotates in just 5.5 days, and produces X-ray emission 4,000 times greater than the sun does at solar maximum. These rare stars were found as part of an X-ray survey of the original Kepler field of view, a patch of the sky comprising parts of the constellations Cygnus and Lyra.
Rapidly Rotating, X-ray Bright Stars in the Kepler Field (DOI: 10.3847/0004-637X/831/1/27) (DX) (arXiv:1608.07828)
NASA will hold a media briefing at 11 a.m. EDT Monday, June 19, to announce the latest planet candidate results from the agency's exoplanet-hunting Kepler mission. The briefing, taking place during the Kepler Science Conference, will be held at NASA's Ames Research Center in California's Silicon Valley.
That will kick off the fourth Kepler Science Conference from June 19-23 at NASA's Ames Research Center in California.
Google's research team Google AI has applied machine learning to data from NASA's Kepler space observatory, finding an 8th exoplanet orbiting Kepler-90 (2,545 ly away). The team also found a sixth exoplanet orbiting Kepler-80 (1,100 ly away):
Our solar system now is tied for most number of planets around a single star, with the recent discovery of an eighth planet circling Kepler-90, a Sun-like star 2,545 light years from Earth. The planet was discovered in data from NASA's Kepler Space Telescope.
The newly-discovered Kepler-90i – a sizzling hot, rocky planet that orbits its star once every 14.4 days – was found using machine learning from Google. Machine learning is an approach to artificial intelligence in which computers "learn." In this case, computers learned to identify planets by finding in Kepler data instances where the telescope recorded signals from planets beyond our solar system, known as exoplanets.
[...] Kepler-90i wasn't the only jewel this neural network sifted out. In the Kepler-80 system, they found a sixth planet. This one, the Earth-sized Kepler-80g, and four of its neighboring planets form what is called a resonant chain – where planets are locked by their mutual gravity in a rhythmic orbital dance. The result is an extremely stable system, similar to the seven planets in the TRAPPIST-1 system.
Their research paper reporting these findings has been accepted for publication in The Astronomical Journal. [Christopher] Shallue and [Andrew] Vanderburg plan to apply their neural network to Kepler's full set of more than 150,000 stars.
The size of Kepler-90i is estimated at 1.32 ± 0.21 Earth radii. Surface temperature is estimated at 435°C (709 K).
Kepler-80g is likely smaller at 1.13 ± 0.14 Earth radii, with a cooler surface temperature of 144°C (418 K).
The outermost known exoplanet in the Kepler-90 system, Kepler-90h, has a mass under 1.2 Jupiter masses and a temperature of around 292 K (19 °C; 66 °F), so it may be a good candidate for hosting life on a moon.
NASA will host a Reddit AMA at 3 PM EST to discuss the findings.
Also at University of Texas at Austin.
A system of at least five exoplanets has been discovered by citizen scientists through a project called Exoplanet Explorers, part of the online platform Zooniverse, using data from NASA's Kepler space telescope. This is the first multi-planet system discovered entirely through crowdsourcing. A study describing the system has been accepted for publication in The Astronomical Journal.
Thousands of citizen scientists got to work on Kepler data in 2017 when Exoplanet Explorers launched. It was featured on a program called Stargazing Live on the Australia Broadcasting Corporation (ABC). On the final night of the three-day program, researchers announced the discovery of a four-planet system. Since then, they have named it K2-138 and determined that it has a fifth planet -- and perhaps even a sixth, according to the new paper.
The K2-138 System: A Near-resonant Chain of Five Sub-Neptune Planets Discovered by Citizen Scientists (open, DOI: 10.3847/1538-3881/aa9be0) (DX) (arXiv)
Data from the Kepler spacecraft's extended mission has been used to confirm 95 new exoplanet discoveries:
"We started out analyzing 275 candidates of which 149 were validated as real exoplanets. In turn 95 of these planets have proved to be new discoveries," said American PhD student Andrew Mayo at the National Space Institute (DTU Space) at the Technical University of Denmark.
[...] The Kepler spacecraft was launched in 2009 to hunt for exoplanets in a single patch of sky, but in 2013 a mechanical failure crippled the telescope. However, astronomers and engineers devised a way to repurpose and save the space telescope by changing its field of view periodically. This solution paved the way for the follow up K2 mission, which is still ongoing as the spacecraft searches for exoplanet transits.
[...] One of the planets detected was orbiting a very bright star. "We validated a planet on a 10 day orbit around a star called HD 212657, which is now the brightest star found by either the Kepler or K2 missions to host a validated planet. Planets around bright stars are important because astronomers can learn a lot about them from ground-based observatories," said Mayo.
275 candidates and 149 validated planets orbiting bright stars in K2 campaigns 0-10 (open, DOI: 10.3847/1538-3881/aaadff) (DX)
This work, in addition to increasing the population of validated K2 planets by more than 50% and providing new targets for follow-up observations, will also serve as a framework for validating candidates from upcoming K2 campaigns and the Transiting Exoplanet Survey Satellite (TESS), expected to launch in 2018.
Submitted via IRC for Fnord666
The Kepler planet-hunting telescope was designed to do one thing: gather data from a single portion of the sky often enough to catch rare, brief events. The events it was looking for were slight dips in light that happened as a planet passed in between its host star and Earth. But it captured other transient events as well. Some of these other events were supernovae—the explosion of massive stars—and Kepler captured two just as the explosion burst through their surface.
But at least one of the brief events Kepler observed was so odd it wasn't originally recognized as a supernova. It was only after the observatory's data was released to the entire research community that people started proposing that something so bright was most likely a supernova. Now, researchers are offering an analysis of why this event looked so strange.
[...] So what was so odd about KSN 2015K? While the object was clearly bright enough to be a supernova, it was on an accelerated schedule, taking only two days to reach peak brightness. It was already fading out after only a week, and it was gone at three weeks. By contrast, another recent supernova was still brightening roughly two weeks after it was first detected. More generally, this new event was about eight times faster than we'd expect from a type Ia supernova. This makes KSN 2015K a "fast evolving luminous transient," or FELT.
Also at The Register.
A fast-evolving luminous transient discovered by K2/Kepler (DOI: 10.1038/s41550-018-0423-2) (DX)
Update 2: SpaceX's live coverage starts at 6:36 PM EDT (22:36 UTC).
Update 3: TESS successfully separated from Falcon 9 and was deployed into a highly elliptical orbit.
NASA's Transiting Exoplanet Survey Satellite (TESS) mission is set to launch
on April 16 at 6:32 PM ET (22:32 UTC) aboard a Falcon 9 rocket from SLC-40, Cape Canaveral Air Force Station, Florida. The spacecraft was developed by MIT with seed funding in Google back in 2008. The spacecraft will perform an all-sky survey using four 24° × 24° wide field-of-view cameras that can image a total of 24° × 96° (2,304 square degrees) of sky every 30 minutes (the Sun and Moon are only about 0.2 deg2 to Earth-based observers).
TESS will use a unique "P/2" 2:1 lunar resonant orbit to image stars in both the Northern and Southern hemispheres. The survey will image 26 observation sectors of 24° × 96° each, with some overlap at the ecliptic poles. The total survey area will be about 400 times larger than the area searched by the Kepler mission.
TESS will study about 500,000 stars, including the nearest 1,000 red dwarfs, with the goal of finding at least 3,000 new transiting exoplanet candidates. The spacecraft will study F, G, K and M type stars (spanning from F5 to M5), some of which are 30-100 times brighter than stars surveyed by the Kepler spacecraft. Many of the stars will be much closer to Earth than stars surveyed by Kepler, allowing for easier confirmation and follow-up measurements of exoplanets. 30-minute full-frame exposures will be used to search for transient events such as supernovae, star flares, and gamma-ray bursts.
Each observation sector will only be viewed for 27 days (at least in the initial phase of the mission), which will limit the exoplanets seen to those with shorter orbital periods. Potentially habitable exoplanet candidates will likely be found around red dwarfs rather than Sun-like stars. However, TESS's own orbit should remain stable for decades, which could mean that its mission will be extended to allow for a greater variety of exoplanets to be found.
Earlier this week, NASA's Kepler team received an indication that the spacecraft fuel tank is running very low. NASA has placed the spacecraft in a hibernation-like state in preparation to download the science data collected in its latest observation campaign. Once the data has been downloaded, the expectation is to start observations for the next campaign with any remaining fuel.
[...] To bring the data home, the spacecraft must point its large antenna back to Earth and transmit the data during its allotted Deep Space Network time, which is scheduled in early August. Until then, the spacecraft will remain stable and parked in a no-fuel-use safe mode. On August 2, the team will command the spacecraft to awaken from its no-fuel-use state and maneuver the spacecraft to the correct orientation and downlink the data. If the maneuver and download are successful, the team will begin its 19th observation campaign on August 6 with the remaining fuel.
Related: Google Researchers Discover an 8th Planet in the Kepler-90 System
Citizen Scientists Credited for Discovery of Multi-Planet System
Kepler's K2 Mission Going Strong With Another 95 New Exoplanets Confirmed
NASA's TESS Mission Set to Launch on Wednesday, April 18
Scientists have shown that water is likely to be a major component of those exoplanets (planets orbiting other stars) which are between two to four times the size of Earth. It will have implications for the search of life in our Galaxy. The work is presented at the Goldschmidt conference in Boston.
[...] [A] new evaluation of data from the exoplanet-hunting Kepler Space Telescope and the Gaia mission indicates that many of the known planets may contain as much as 50% water. This is much more than the Earth's 0.02% (by weight) water content. [...] Scientists have found that many of the 4000 confirmed or candidate exoplanets discovered so far fall into two size categories: those with the planetary radius averaging around 1.5 that of the Earth, and those averaging around 2.5 times the radius of the Earth.
[...] "We have looked at how mass relates to radius, and developed a model which might explain the relationship," said [lead researcher] Li Zeng. The model indicates that those exoplanets which have a radius of around x1.5 Earth radius tend to be rocky planets (of typically x5 the mass of the Earth), while those with a radius of x2.5 Earth radius (with a mass around x10 that of the Earth) are probably water worlds."
"This is water, but not as commonly found here on Earth," said Li Zeng. "Their surface temperature is expected to be in the 200 to 500 degree Celsius range. Their surface may be shrouded in a water-vapor-dominated atmosphere, with a liquid water layer underneath. Moving deeper, one would expect to find this water transforms into high-pressure ices before we reaching the solid rocky core. The beauty of the model is that it explains just how composition relates to the known facts about these planets." Li Zeng continued, "Our data indicate that about 35% of all known exoplanets which are bigger than Earth should be water-rich. These water worlds likely formed in similar ways to the giant planet cores (Jupiter, Saturn, Uranus, Neptune) which we find in our own solar system. The newly-launched TESS mission will find many more of them, with the help of ground-based spectroscopic follow-up. The next generation space telescope, the James Webb Space Telescope, will hopefully characterize the atmosphere of some of them. This is an exciting time for those interested in these remote worlds."
The most recent update explains that Kepler embarked on its 19th observation campaign on Aug. 29. It was woken from "sleep mode" but one of its thrusters exhibited "unusual behaviour". The short update also states that the the telescope's "pointing performance" may be adversely affected.
The space telescope, originally launched in March 2009, has had a tumultuous year. The team placed Kepler into hibernation in July, as their new planet-hunter, the Transiting Exoplanet Survey Satellite (TESS), began testing for its own mission. The hibernation-like state was to ensure that the data from Kepler's 18th mission, stored onboard the spacecraft, would be able to make its way back to Earth.
That data was successfully downloaded on Aug. 9, as NASA monitored Kepler's health before placing it into sleep mode on Aug. 24.
NASA's Dawn mission is drawing to a close after 11 years of breaking new ground in planetary science, gathering breathtaking imagery, and performing unprecedented feats of spacecraft engineering.
Dawn's mission was extended several times, outperforming scientists' expectations in its exploration of two planet-like bodies, Ceres and Vesta, that make up 45 percent of the mass of the main asteroid belt. Now the spacecraft is about to run out of a key fuel, hydrazine. When that happens, most likely between mid-September and mid-October, Dawn will lose its ability to communicate with Earth. It will remain in a silent orbit around Ceres for decades.
[...] Because Ceres has conditions of interest to scientists who study chemistry that leads to the development of life, NASA follows strict planetary protection protocols for the disposal of the Dawn spacecraft. Unlike Cassini, which deliberately plunged into Saturn's atmosphere to protect the system from contamination -- Dawn will remain in orbit around Ceres, which has no atmosphere.
Engineers designed Dawn's final orbit to ensure it will not crash for at least 20 years -- and likely decades longer.
Using the NASA/ESA Hubble Space Telescope and older data from the Kepler Space Telescope two astronomers have found the first compelling evidence for a moon outside our own Solar System. The data indicate an exomoon the size of Neptune, in a stellar system 8000 light-years from Earth. The new results are presented in the journal Science Advances.
[...] In 2017 NASA's Kepler Space Telescope detected hints of an exomoon orbiting the planet Kepler-1625b. Now, two scientists from Columbia University in New York (USA) have used the incomparable capabilities of the NASA/ESA Hubble Space Telescope to study the star Kepler-1625, 8000 light-years away, and its planet in more detail. The new observations made with Hubble show compelling evidence for a large exomoon orbiting the only known planet of Kepler-1625. If confirmed, this would be the first discovery of a moon outside our Solar System.
The candidate moon, with the designation Kepler-1625b-i, is unusual because of its large size; it is comparable in diameter to the planet Neptune. Such gargantuan moons are unknown in our own Solar System.
Other sources put Kepler-1625 at around 4,000 light years away.
Discoveries like this are why we could use as many identical better-than-Hubble space telescopes as we can build and launch.
Evidence for a large exomoon orbiting Kepler-1625b (open, DOI: 10.1126/sciadv.aav1784) (DX)
The tally of potentially habitable alien planets may have to be revised downward a bit. To date, NASA's prolific Kepler space telescope has discovered about 30 roughly Earth-size exoplanets in their host stars' "habitable zone" — the range of orbital distances at which liquid water can likely exist on a world's surface.
Or so researchers had thought. New observations by the European Space Agency's (ESA) Gaia spacecraft suggest that the actual number is probably significantly smaller — perhaps between two and 12, NASA officials said today (Oct. 26)
[...] Gaia's observations suggest that some of the Kepler host stars are brighter and bigger than previously believed, the officials added. Planets orbiting such stars are therefore likely larger and hotter than previously thought.
Also at NASA.
The Kepler Space Telescope (retired in place last year after running out of hydrazine) has racked up over 2600 planetary discoveries in its nine years of operation. Its successor, the Transiting Exoplanet Survey Satellite (TESS) has already found hundreds itself. In 2017 a mysterious gap was identified in the sizes of exoplanets discovered by Kepler (and which continues in those since discovered by TESS.) There are significantly less planets between 1.5 and 2x the size of Earth vs. planets either larger or smaller than that. This has left astronomers puzzling over this peculiar patch of planetary paucity
There are three general theories that attempt to explain the gap.
One possibility [...] is a reverse-Goldilocks scenario in which medium-sized rocky planets with atmospheres can't last. "You are either going to be big enough to hold on to your atmosphere, or if you are intermediate in size, then you are probably not big enough and you are going to lose it all pretty quickly," [astronomer Diana Dragomir] said. "It's like a tug of war; it's really hard to stay in the middle."
Another theory [according to Sara Seager, an astronomer at MIT] holds that the gap results directly from planetary genesis, maybe because of the location or makeup of the gas and dust left over from the star's birth.
[...] a third theory proposes, planets' own cooling processes might cause their atmospheres to evaporate, an effect called "core-powered mass loss.
TESS, which is just getting started, will enable observation of 400 times more sky than Kepler was able to survey and will return data on planets further out from their stars, and also on many nearer stars that can then be observed for followup with Earth based telescopes.
Tiny balls of rock or high gravity super Earths. Time will tell if there really is no place like home.
NASA's Dawn spacecraft has gone silent, ending a historic mission that studied time capsules from the solar system's earliest chapter.
Dawn missed scheduled communications sessions with NASA's Deep Space Network on Wednesday, Oct. 31, and Thursday, Nov. 1. After the flight team eliminated other possible causes for the missed communications, mission managers concluded that the spacecraft finally ran out of hydrazine, the fuel that enables the spacecraft to control its pointing. Dawn can no longer keep its antennae trained on Earth to communicate with mission control or turn its solar panels to the Sun to recharge.
The Dawn spacecraft launched 11 years ago to visit the two largest objects in the main asteroid belt. Currently, it's in orbit around the dwarf planet Ceres, where it will remain for decades.
Pluto and Ceres
After Eight Years, NASA's Dawn Probe Brings Dwarf Planet Ceres Into Closest Focus
NASA's Dawn Orbiter Finds a Mountain on Ceres
Dawn Spies Magnesium Sulphate and Possible Geological Activity on Ceres
Ceres' Cryovolcano Ahuna Mons Formed in the Geologically Recent Past
Ceres's Cryovolcanoes Viscously Relax Into Nothingness
Organic Molecules Found on Ceres
Early Asteroids May Have Been Made of Mud Rather Than Rock
Dawn Mission Extended at Ceres
Ceres May Have Had a Global Surface Ocean in the Past
Bright Areas on Ceres Suggest Geologic Activity
Dawn's Orbit Around Ceres: A New Low
Dawn's Orbit Around Ceres: First Images
Dawn Spacecraft Captures Closest-Ever Images of Ceres' Shiny Occator Crater