K2 News and Results

K1 or K2 ?

https://www.nasa.gov/press-release/nasa-hosts-media-teleconference-to-announce-latest-kepler-discovery

NASA will host a media teleconference at 1 p.m. EST Thursday, Dec. 14, to announce the latest discovery made by its planet-hunting Kepler space telescope. The discovery was made by researchers using machine learning from Google. Machine learning is an approach to artificial intelligence, and demonstrates new ways of analyzing Kepler data

Machine learning? So, a huge batch of candidates or something?

Judging by the caption to the picture, it's from Kepler's primary mission.

http://www.caltech.edu/news/citizen-scientists-discover-five-planet-system-80989

The K2-138 system: A Near-Resonant Chain of Five Sub-Neptune Planets Discovered by Citizen Scientists

Five (may be six) planets in resonance 3:2 !

Paper (free) :
http://iopscience.iop.org/article/10.3847/1538-3881/aa9be0/pdf

Additionally,

An ultra-short period rocky super-Earth with a secondary eclipse and a Neptune-like companion around K2-141
https://arxiv.org/abs/1801.03502

Discovery of a Transiting Adolescent Sub-Neptune Exoplanet in the Cas-Tau Association with K2
https://arxiv.org/abs/1801.07320

Quote :

The role of stellar age in the measured properties and occurrence rates of exoplanets is not well understood. This is in part due to a paucity of young planets and the uncertainties in age-dating for most exoplanet host stars. Exoplanets belonging to coeval stellar populations, young or old, are particularly useful as benchmarks for studies aiming to constrain the evolutionary timescales relevant for planets. Such timescales may concern orbital migration, gravitational contraction, or atmospheric photo-evaporation, among other mechanisms. Here we report the serendipitous discovery of a transiting sub-Neptune from K2 photometry of the low-mass star EPIC 247267267. From multiple age indicators we estimate the age of the star to be in the range of 50-500 Myr at 68% confidence. However, based on its kinematics, we propose the star belongs to the Cas-Tau association, which we suggest has an age of 46 ± 8 Myr. Our newly derived age estimate for the association is based on a color-magnitude diagram analysis of high-probability members near the main sequence turnoff. The size of EPIC 247267267 b (RP=3.0±0.5R⊕) combined with its youth make it an intriguing case study for photo-evaporation models, which predict enhanced atmospheric mass loss during early evolutionary stages.

EPIC229426032 b and EPIC246067459 b: discovery of a highly inflated and a 'regular' pair of transiting hot Jupiters from K2
https://arxiv.org/abs/1801.07959

Sirius_Alpha wrote:

Additionally,

An ultra-short period rocky super-Earth with a secondary eclipse and a Neptune-like companion around K2-141
https://arxiv.org/abs/1801.03502

There seems to be another paper about K2-141 coming out, following is listed on A&A forthcoming:

Quote :

K2-141 b. A 5-M_oplus super-Earth transiting a K7 V star every 6.7 hours
O. Barragán, D. Gandolfi, F. Dai, J. Livingston, C. M. Persson, T. Hirano, N. Narita, Sz. Csizmadia, J. N. Winn, D. Nespral, J. Prieto-Arranz, A. M. S. Smith, G. Nowak, S. Albrecht, G. Antoniciello, A. Bo Justesen, J. Cabrera, W. D. Cochran, et al.
A&A, Forthcoming article
Received: 31 October 2017 / Accepted: 11 January 2018
DOI: https://doi.org/10.1051/0004-6361/201732217

Updated parameters for K2-28 from Spitzer:

Chen et al. "An Improved Transit Measurement for a 2.4 R_Earth Planet Orbiting A Bright Mid-M Dwarf K2-28"
https://arxiv.org/abs/1801.10177

More planets from K2 mission
https://www.sciencedaily.com/releases/2018/02/180215105756.htm

Awesome! Of note is a 2.8 R_e planet around HD 212657 (given the designation K2-167). At V = 8.24±0.01, this will be a useful system to study super-Earth atmospheres.

Paper : http://outer.space.dtu.dk/awm/images/validationpaper.pdf

275 CANDIDATES AND 149 VALIDATED PLANETS ORBITING BRIGHT STARS IN K2 CAMPAIGNS 0-10

Doppler detection of two of the K2-3 planets.

Eyes on K2-3: A system of three likely sub-Neptunes characterized with HARPS-N and HARPS
https://arxiv.org/abs/1802.08320

EPIC247098361b: a transiting warm Saturn on an eccentric P=11.2 days orbit around a V=9.9 star
https://arxiv.org/abs/1802.08865

Quote :

We report the discovery of EPIC247098361b using photometric data of the Kepler K2 satellite coupled with ground-based spectroscopic observations. EPIC247098361b has a mass of MP=0.397±0.037 MJ, a radius of RP=1.00±0.020 RJ, and a moderately low equilibrium temperature of Teq=1030±15 K due to its relatively large star-planet separation of a=0.1036 AU. EPIC247098361b orbits its bright (V=9.9) late F-type host star in an eccentric orbit (e=0.258±0.025) every 11.2 days, and is one of only four well characterized warm Jupiters having hosts stars brighter than V=10. We estimate a heavy element content of 20 ± 7 M⊕ for EPIC247098361b, which is consistent with standard models of giant planet formation. The bright host star of EPIC247098361b makes this system a well suited target for detailed follow-up observations that will aid in the study of the atmospheres and orbital evolution of giant planets at moderate separations from their host stars.

Kepler detects Earth-radius planet 1 AU from G-type star.

Sirius_Alpha wrote:

Kepler detects Earth-radius planet 1 AU from G-type star.

A chance to discover yourself...

Orbiting a naked-eye visible star, too. Hopefully there won't be too much controversy related to characterising its atmosphere.

Two warm, low-density sub-Jovian planets orbiting bright stars in K2 campaigns 13 and 14
https://arxiv.org/abs/1803.02858

Quote :

We report the discovery of two planets transiting the bright stars HD 89345 (EPIC 248777106, V = 9.376, K = 7.721) in K2 Campaign 14 and HD 286123 (EPIC 247098361, V = 9.822, K = 8.434) in K2 Campaign 13. Both stars are G-type stars, one of which is at or near the end of its main sequence lifetime, and the other that is just over halfway through its main sequence lifetime. HD 89345 hosts a warm sub-Saturn (0.616 R_J, 0.103 M_J, T_eq = 1059 K) in an 11.81-day orbit. The planet is similar in size to WASP-107b, which falls in the transition region between ice giants and gas giants. HD 286123 hosts a Jupiter-sized, low-mass planet (1.080 R_J, 0.408 M_J, T_eq = 999 K) in an 11.17-day, mildly eccentric orbit, with e = 0.268+/-0.037. Given that they orbit relatively evolved main-sequence stars with ages of ~5-7 Gyr, and have orbital periods longer than 10 days, these planets are interesting candidates for studies of gas planet evolution, migration, and (potentially) re-inflation. Both planets have spent their entire lifetimes near the proposed stellar irradiation threshold at which giant planets become inflated, and neither shows any sign of radius inflation. They probe the regime where inflation begins to become noticeable and are valuable in constraining planet inflation models. In addition, the brightness of the host stars, combined with large atmospheric scale heights of the planets, makes these two systems exceptionally favorable targets for transit spectroscopy to study their atmospheres and perhaps provide insight into the physical mechanisms that that lead to inflated hot Jupiters.

https://phys.org/news/2018-03-planets-cool-dwarf-stars.html

Quote :

15 new planets confirmed around cool dwarf stars

"One of the brightest red dwarfs, K2-155 that is around 200 light years away from Earth, has three transiting super-Earths...the outermost planet, K2-155d, with a radius 1.6 times that of Earth, could be within the host star's habitable zone."

"The researchers found that K2-155d could potentially have liquid water on its surface based on three-dimensional global climate simulations. A more precise estimate of the radius and temperature of the K2-155 star would be needed to conclude definitively whether K2-155d is habitable. Achieving such precision would require further studies, for example, using interferometric techniques."

https://www.nasa.gov/feature/ames/nasa-s-kepler-spacecraft-nearing-the-end-as-fuel-runs-low

NASA’s Kepler Spacecraft Nearing the End as Fuel Runs Low

Three small planets transiting the bright young field star EPIC 249622103
https://arxiv.org/abs/1803.05056

Quote :

We report the detection of three small transiting planets around the young K3 dwarf EPIC 249622103 (2MASS J15215519-2013539) from observations during Campaign 15 of the K2 mission. The star is relatively nearby (d = 69 pc) and bright (V = 10.7 mag, Ks = 8.4 mag), making the planetary system an attractive target for radial velocity follow-up and atmospheric characterization with the James Webb Space Telescope. The inner two planets are hot super-Earths (Rb = 1.40 ± 0.06 R⊕, Rc = 1.34 ± 0.08 R⊕), while the outer planet is a warm sub-Neptune (Rd = 2.6 ± 0.1 R⊕). We estimate the stellar age to be 360+490−140 Myr based on rotation, activity, and kinematic indicators. The EPIC 249622103 system is particularly interesting given recent evidence for inflated radii in planets around similarly-aged stars, a trend potentially related to photo-evaporation, core-cooling, or both mechanisms.

Led_Zep wrote:

https://www.nasa.gov/feature/ames/nasa-s-kepler-spacecraft-nearing-the-end-as-fuel-runs-low

NASA’s Kepler Spacecraft Nearing the End as Fuel Runs Low

All good things...

Still, it's had a pretty good run, no?

A sub-Neptune in the 3-billion-year-old open cluster Ruprecht 147.

Curtis et al., "K2-231 b: A sub-Neptune exoplanet transiting a solar twin in Ruprecht 147"
https://arxiv.org/abs/1803.07430

K2-229b is a very dense planet in a multiple planet system.

An Earth-sized exoplanet with a Mercury-like composition
https://www.nature.com/articles/s41550-018-0420-5

This tweet thread has more graphics and information.
https://twitter.com/exohugh/status/978308332976066560

News release about K2-229: http://spaceref.com/extrasolar-planets/newly-discovered-planet-is-hot-metallic-and-dense-as-mercury.html

On a non-exoplanet-related topic, K2 also has been useful for studying Fast-Evolving Luminous Transients, which are identified as supernovae exploding within dust shells: http://spaceref.com/astronomy/kepler-solves-mystery-of-fast-and-furious-explosions.html