Welcome to the Virtual Planetary Laboratory
Jacob Haqq-Misra joins Far Infrared Surveyor team
VPL member Jacob Haqq-Misra has recently joined the science and technology definition team (STDT) for the Far Infrared Surveyor mission concept being studied by NASA to help identify exoplanet science goals. Congratulations Jacob! MORE>
VPL members comment on ancient air caught by shooting stars
A News & Views article in Nature by VPL members Kevin Zahnle and Roger Buick discusses a recent paper arguing that ashes of ancient meteors recovered in a 2.7-billion-year-old lake bed imply that Earth's upper atmosphere was rich in oxygen at a time when all other evidence implies the atmosphere was oxygen-free MORE>
"Limit Cycles" can reduce the width of the habitable zone
A recent paper by VPL members Jacob Haqq-Misra, Ravi Kopparapu, Natasha Batalha, Chester "Sonny" Harman, and Jim Kasting argues that terrestrial planets can maintain above-freezing conditions through cycling of CO2 in the atmosphere and crust, and recent calculations have suggested that planets near the outer edge of the habitable zone can oscillate between snowball states and warm states. Modeling work by these authors suggests that limit cycles such as this can occur, but previous calculations may have over-estimated their importance. Limit cycles can occur for planets orbiting sun-like stars for planets with CO2 outgassing rates similar to modern Earth, but limit cycling does not occur on planets orbiting dimmer stars. This work suggests that parent star type, volcanic activity, and seafloor weathering are important factors to consider for planetary habitability. MORE>
The outer edge of the habitable zone is affected by limits on CO2 outgassing rates
In this recent paper by VPL member Dr. Dorian Abbot, simple equations are used to estimate the climate and CO2 budget of a planet near the outer edge of the habitable zone. Planets near the outer edge of the habitable zone may not be able to stay warm if CO2 outgassing rates are insufficient to maintain a large amount of atmospheric CO2 against removal processes by silicate weathering. This work derives an analytical limit to the outer edge of the habitable zone based on these processes and shows that climate cycles between snowball and warm states are possible beyond the outer edge if the weathering rate in the snowball state is smaller than the CO2 outgassing rates. MORE>
Congratulations to recent VPL NPPs!
Three VPL students have recently been awarded fellowships by the NASA Postdoctoral Program! Peter Gao and Giada Arney were awarded NPPs to work at NASA Ames and NASA Goddard, respectively. Eddie Schwieterman has been awarded a NAI NPP to work with the NAI team at UC Riverside. Congratulations to all! MORE>
PNAS Habitable Zone feature includes VPL scientists
Understanding planetary habitability is important for characterizing exoplanets and selecting targets for future exoplant observing missions. One of the key issues relevant to planetary habitability is the concept of the "habitable zone." A recent feature in PNAS on the habitable zone features commentary by VPL scientists Shawn Domagal-Goldman, Ravi Kopparapu, Jim Kasting, and Ray Pierrehumbert. Also featured is a figure showing the Habitable Zone by VPL grad student Sonny Harman. MORE>
Congratulations to Shawn Domagal-Goldman!
VPL member Shawn Domagal-Goldman at NASA Goddard Space Flight Center has been honored with the Agency Early Career Achievement Medal! Congratulations, Shawn! MORE>
Early earth's air pressure was less than half of today's
A new study led by VPL researcher Sanjoy Som together with VPL members Roger Buick and David Catling and others implies that early Earth's atmospheric pressure 2.7 billion years ago was less than half of modern day. The researchers used gas bubbles trapped in ancient sea-level lava flows as a "paleobarometer". The sizes of the bubbles record the pressure of the atmosphere bearing down on the cooling lava billions of years ago. This low atmospheric pressure suggests that early microbes may have been consuming atmospheric nitrogen, but there was not an efficient process to release that consumed nitrogen back to the atmosphere like there is today. MORE>
Congratulations to Rory Barnes!
Rory Barnes of the UW astronomy department has been promoted to an Assistant Professor in astrobiology! Congratulations Rory! MORE>
Congratulations to new members of NASA STDTs!
NASA has convened Science and Technology Definitions Teams (STDTs) to study large telescope concepts for future direct imaging of exoplanets. Congratulations to Vikki Meadows, Tyler Robinson, and Shawn Domagal-Goldman who have been seletected as members of these teams! Vikki will be a member of the LUVIOR team, and Shawn will be the LUVIOR Deputy Study Scientist. Shawn is also a member of the HabEx STDT, as is Ty Robinson. Congratulations to all! MORE>
Dry planets help weed out false positive biosignatures
Terrestrial planets orbiting in the habitable zones of low mass stars may be extremely dry due to water loss from exposure to high energy UV radiation during their host stars' early evolution. VPL researchers Peter Gao, Tyler Robinson, Yuk Yung, and collaborators show that if such a planet outgassed a secondary atmosphere composed primarily of CO2, UV radiation can break up the CO2 molecules and produce large amounts of abiotic O2 and O3. O2 produced by this mechanism can reach up to 20% of the atmosphere if large amounts of water are lost. However, this should not present a great challenge for deciphering between biological and abiotic oxygen in an exoplanet atmosphere: the researchers show that the lack of water in the reflectance and emission spectra of these worlds clearly indicate that the oxygen signals are likely abiotic in nature. MORE>
Hints from selenium isotopes on the end-Permian mass extinction
VPL members Eva Stüeken, Roger Buick, and collabors studied isotope ratios of selenium, a trace element. Their results show that biological productivity of macro-organisms collapsed during the Permian-Triassic mass extinction, but the collapse was probably not caused by a shortage of nutrients. Other factors such as ocean acidification or perturbations of food webs may have been more important. MORE>
Congratulations to Aomawa Shields!
VPL member Aomawa Shields has been awarded the 2016 ASU Origins Project Postdoctoral Lectureship Award! This prestigous $10,000 award is offered to young scientists based on scholarly achievement and skills in science communication. Shields, who has a professional acting background in addition to her rigorous training as a scientist, will be resident at Arizona State University for a week and will offer a series of departmental colloquia and a large public lecture in early April. Congratulations Aomawa! MORE>
Dead or Alive? New ways to sniff out imposter biosignatures
Recent research has shown that planets orbiting cool stars are potentially susceptible to the accumulation of oxygen through abiotic processes. This is problematic as oxygen is considered an important target biosignature for future exoplanet observing missions. However, in a new study VPL researchers including doctoral student Edward Schwieterman and principal investigator Victoria Meadows have now shown that these “biosignature impostors” are accompanied by other signatures that would indicate their abiotic origin. If abiotic oxygen is produced through CO2 photolysis, CO would also be also be observable in transit transmission observations. If the abiotic oxygen is from a history of massive hydrogen escape, the substantial oxygen atmosphere that would remain could be identified by pressure-sensitive O4 features in transmission or reflected light observations. The paper has been accepted to the Astrophysical Journal Letters. VPL graduate students Giada Arney, Rodrigo Luger, Sonny Harman and researchers Shawn Domagal-Goldman, Drake Deming, Amit Misra, and Rory Barnes also contributed. A press release about this work can be found here. MORE>
Water clouds do not cool planets around low mass stars as much as previously believed
Planets in the habitable zone of low-mass, cool stars are expected to be in synchronous rotation, where one side of the planet always faces the host star. Previous studies using 3-D climate models have shown that, if a planet orbiting these low-mass stars is slowly rotating, thick water clouds form at substellar point (the point at which the star is directly overhead) increasing the reflectivity, and thus stabilizing the planet against increased warming at the inner edge of the habitable zone. However these studies did not use self-consistent orbital/rotational periods for synchronously rotating planets placed at different distances from the host star. VPL researchers Ravi Kopparapu, Jacob Haqq-Misra, Vikki Meadows and Jim Kasting, along with collaborator Eric Wolf, have shown that, using correct relations between orbital and rotational periods, the inner edge of the HZ around low mass, cool stars is not as close as the estimates from previous studies. MORE>
Geothermal heating enhances atmospheric asymmetries on synchronously rotating planets
Earth-like planets that orbit small, red stars (M-dwarfs) might be able to sustain liquid water on the surface and provide habitable conditions where life could develop. However, such planets orbit their parent star so closely that they are prone to fall into synchronous rotation so that one side of the planet always faces the star and is constantly heated. Their atmospheres can be at risk of collapsing into huge ice caps on the anti-stellar side, but the large-scale motions of the atmosphere can provide enough energy transport from the warm side to the cold side to keep the climate stable.VPL researchers Jacob Haqq-Misra and Ravi Kopparapu used a 3D climate model and found that geothemal heating from tides can warm the planets' night sides. The reasearchers find that cross-polar circulation can transport energy and mas from the day side to night side, contributing to climate stability. MORE>
Rare and abundant microbial lineages in deep-sea hydrothermal vents
In every ecosystem studied to date, microbial diversity generally consists of a few dominant species, and many thousand rare species. However, we don't have a good understanding of what those rare groups are doing, or how they're distributed throughout the environment. VPL researchers Dr. Rika Anderson and Dr. John Baross examined the global distribution of rare and abundant microbial species in hydrothermal vent systems across the globe. They found that the abundant species tend to be the most successful taking over a given community as well as traveling across the globe-- they're both dominant and cosmopolitan. In contrast, the rare species are homebodies. They tend to appear in small numbers where they are found, and those rare groups don't travel around much. MORE>
The global selenium cycle
VPL researchers Eva Stüeken, Roger Buick, David Catling, and coauthors studied trends in selenium cycling over Earth's history and proposed a conceptual model, supported by data, of how the selenium cycle operates in the modern ocean. Their model supports the idea of oxidative weathering in the late Archean, before the Great Oxidation Event when oxygen levens in the atmosphere rose. Lastly, the data are consistent with an anoxic ocean throughout most of the Precambrian and oxygenation of the deep ocean in the Neoproterozoic. This work helped establish selenium isotopes as a biogeochemical redox proxy that we can now use to address astrobiological questions. MORE>
A whiff of ancient oxygen supported by selenium isotopes
VPL researchers Eva Stüeken, Roger Buick, and Arial Anbar showed that there was a brief interval around 2.5 billion years ago when the flux of selenium into the ocean increased and isotopes were more fractionated. These data support previous indications that this period corresponds to a brief "whiff" of free oxygen, either globally or within microbial mats on land. Hence oxygen production must have started long before the great oxidation event at ~2.3-2.4 billion years ago, which in turn supports the idea that it takes a considerable amount of time to fully oxidize the surface of a planet, which has implications for the evolution of organisms that require oxygen to breathe. MORE>
The unusual architecture of the υ Andromedae planetary system
The star υ Andromedae has 3 known planets orbiting it, all three close to or greater than the size of Jupiter. Surprisingly, observations show that the orbits of the outer two planets are tilted relative to each other by about 30 degrees, which is very unusual in comparison with the solar system. A study led by VPL graduate student Russell Deitrick together with VPL members Rory Barnes, Tom Quinn, and Rodrigo Luger used computer models to learn more about this interesting planetary system. The researchers were able to place constraints on the inner-most planet's mass and orbital tilt, which were previously unknown. They found that the inner-most planet is likely to be several Jupiter masses, and its orbital plane is probably aligned about halfway between the planes of the outer two planets. MORE>
Abiotic oxygen on exoplanets spells trouble for life-detection
Life has produced significant impacts on our own planet, including the oxygen we breathe, which makes up 21% of Earth's atmosphere. But what would happen if an early, lifeless Earth had been orbiting a different star? VPL Researchers Sonny Harman, Edward Schwieterman, and James Kasting examined what would happen if the early Earth was orbiting around different stars, ranging from a star slightly more massive than the Sun (an F type star) to a star less than half the mass of the Sun (an M type star). For the Earths orbiting smaller stars, the interaction between the atmosphere of the planet and the radiation from the star meant that some abiotic oxygen was produced. This could mean that when we look at distant planets around some types of stars, the presence of oxygen alone may not be a sure sign of life. MORE>
Is the pale blue dot unique?
Voyager 1's iconic image of the Pale Blue Dot shows hints of Earth's uniqueness are visible from great distances; the pale blue color of Earth sets it apart from other objects in our Solar System. But could planet color be used to easily identify Earth-like exoplanets? VPL graduate students Joshua Krissansen-Totton, Edward Schwieterman, Giada Arney, and VPL researchers Tyler Robinson, Benjamin Charnay, Victoria Meadows, and David Catling have authored a paper on whether color can be used to distinguish Earth-like exoplanets from uninhabitable worlds. This paper shows that numerous uninhabitable planets - particularly icy worlds with thick atmospheres - could mimic the Earth's pale blue color. It is possible to distinguish these icy worlds from Earth-like planets with extremely precise color observations, but this level precision demands a lot of telescope time. This suggests that spectral observations may be preferable to color observations for identifying Earth-like exoplanets. MORE>