We search for escaping helium from the hot super Earth 55 Cnc e by taking high-resolution spectra of the 1083 nm line during two transits using Keck/NIRSPEC. We detect no helium absorption down to a 90\% upper limit of 250 ppm in excess absorption or 0.27 milli-Angstrom in equivalent width. This corresponds to a mass loss rate of less than $\sim10^9$ g/s assuming a Parker wind model with a plausible exosphere temperature of 5000-6000 K, although the precise constraint is heavily dependent on model assumptions. We consider both hydrogen- and helium-dominated atmospheric compositions, and find similar bounds on the mass loss rate in both scenarios. Our hydrodynamical models indicate that if a lightweight atmosphere exists on 55 Cnc e, our observations would have easily detected it. Together with the non-detection of Lyman $α$ absorption by Ehrenreich et al 2012, our helium non-detection indicates that 55 Cnc e either never accreted a primordial atmosphere in the first place, or lost its primordial atmosphere shortly after the dissipation of the gas disk.
Observational evidence for escaping exoplanet atmospheres has been obtained for a few exoplanets to date. It comes from strong transit signals detected in the ultraviolet, most notably in the wings of the hydrogen Lyman-$α$ (Ly$α$) line. However, the core of the Ly$α$ line is often heavily affected by interstellar absorption and geocoronal emission, limiting the information about the atmosphere that can be extracted from that part of the spectrum. Transit observations in atomic lines that are (a) sensitive enough to trace the rarefied gas in the planetary wind and (b) do not suffer from signif…
Helium escaping from the atmosphere of a nearby rocky exoplanet orbiting in a habitable zone
Harvard University（哈佛大学）；Carnegie Science Observatories（卡内基科学天文台）；Center for Astrophysics, Harvard & Smithsonian（哈佛-史密森天体物理中心）；School of Engineering and Applied Sciences, Harvard University（哈佛工程学院与应用科学学院）；Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology（麻省理工学院卡弗里天体物理学与空间研究所）；Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology（麻省理工学院地球、大气和行星科学系）；Earth and Planets Laboratory, Carnegie Institution for Science（卡内基科学机构地球与行星实验室）；Space Telescope Science Institute（太空望远镜科学研究所）；Department of Physics & Astronomy, Johns Hopkins University（约翰斯·霍普金斯大学物理与天文系）；Department of Physics, Washington University（华盛顿大学物理系）
JWST is here. The early release observation program (ERO) provides us with the first look at the scientific data and the spectral capabilities. One of the targets from ERO is HAT-P-18b, an inflated Saturn-mass planet with an equilibrium temperature of $\sim$850K. We present the NIRISS/SOSS transmission spectrum of HAT-P-18b from 0.6 to 2.8$μm$ and reveal the planet in the infrared beyond 1.6$μm$ for the first time. From the spectrum, we see clear water and escaping helium tail features in an otherwise very hazy atmosphere. Our free chemistry retrievals with ATMO show moderate Bayesian evidence…
We report helium absorption from the escaping atmosphere of TOI 560.01 (HD 73583b), a $R=2.8 R_\oplus$, $P=6.4$ d mini Neptune orbiting a young ($\sim$600 Myr) K dwarf. Using Keck/NIRSPEC, we detect a signal with an average depth of $0.68 \pm 0.08$% in the line core. The absorption signal repeats during a partial transit obtained a month later, but is marginally stronger and bluer, perhaps reflecting changes in the stellar wind environment. Ingress occurs on time, and egress occurs within 12 minutes of the white light egress, although absorption rises more gradually than it declines. This sugg…
We present the detection of helium in the extended atmosphere of the sub-Saturn WASP-107b using high resolution ($R \approx 25000$) near-infrared spectra from Keck II/NIRSPEC. We find peak excess absorption of $7.26 \pm 0.24\%$ (30$σ$) centered on the HeI triplet at 10833A. The amplitude and shape of the helium absorption profile is in excellent agreement with previous observations of escaping helium from this planet made by CARMENES and HST. This suggests there is no significant temporal variation in the signature of escaping helium from the planet over a two year baseline. This result demons…
Helium is the second-most abundant element in the Universe after hydrogen and is one of the main constituents of gas-giant planets in our Solar System. Early theoretical models predicted helium to be among the most readily detectable species in the atmospheres of exoplanets, especially in extended and escaping atmospheres. Searches for helium, however, have hitherto been unsuccessful. Here we report observations of helium on an exoplanet, at a confidence level of 4.5 standard deviations. We measured the near- infrared transmission spectrum of the warm gas giant WASP-107b and identified the nar…
Large-scale exoplanet search surveys have shown evidence that atmospheric escape is a ubiquitous process that shapes the evolution and demographics of planets. However, we lack a detailed understanding of this process because very few exoplanets discovered to date could be probed for signatures of atmospheric escape. Recently, the metastable helium triplet at 1.083 $μ$m has been shown to be a viable window for the presence of He-rich escaping envelopes around short-period exoplanets. Our objective is to use, for the first time, the Phoenix spectrograph to search for helium in the upper atmosph…
Probing the evaporation of exoplanet atmospheres is key to understanding the formation and evolution of exoplanetary systems. The main tracer of evaporation in the UV is the Lyman-alpha transition, which can reveal extended exospheres. Recently, NIR metastable helium triplet (1.08 microns) revealed extended thermospheres in several exoplanets, opening a new window into evaporation. We aim at spectrally resolving the first helium absorption signature detected in WASP-107b with HST/WFC3. We obtained one transit of WASP-107b with the high-resolution spectrograph CARMENES. We detect an excess heli…
The helium absorption triplet at a wavelength of 10,833 Å has been proposed as a way to probe the escaping atmospheres of exoplanets. Recently this feature was detected for the first time using Hubble Space Telescope (HST) WFC3 observations of the hot Jupiter WASP-107b. We use similar HST/WFC3 observations to detect helium in the atmosphere of the hot Neptune HAT-P-11b at the $4σ$ confidence level. We compare our observations to a grid of 1D models of hydrodynamic escape to constrain the thermospheric temperatures and mass loss rate. We find that our data are best fit by models with high mass …
The magnetic fields of the solar system planets provide valuable insights into the planets' interiors and can have dramatic consequences for the evolution of their atmospheres and interaction with the solar wind. However, we have little direct knowledge of magnetic fields in exoplanets. Here we present a method for detecting magnetic fields in the atmospheres of close-in exoplanets based on spectropolarimetric transit observations at the wavelength of the helium line at 1083 nm. This methodology has been successfully applied before for exploring magnetic fields in solar coronal filaments. Stro…
Early in their lives, planets endure extreme amounts of ionizing radiation from their host stars. For planets with primordial hydrogen and helium-rich envelopes, this can lead to substantial mass loss. Direct observations of atmospheric escape in young planetary systems can help elucidate this critical stage of planetary evolution. In this work, we search for metastable helium absorption---a tracer of tenuous gas in escaping atmospheres---during transits of three planets orbiting the young solar analogue V1298 Tau. We characterize the stellar helium line using HET/HPF, and find that it evolves…
Hydrogen and helium transmission signals trace the upper atmospheres of hot gas-giant exoplanets, where the incoming stellar extreme ultraviolet and X-ray fluxes are deposited. Further, for the hottest stars, the near-ultraviolet excitation of hydrogen in the Balmer continuum may play a dominant role in controlling the atmospheric temperature and driving photoevaporation. KELT-9 b is the archetypal example of such an environment as it is the hottest gas-giant exoplanet known to date (T$_{eq}$ $\sim$ 4500 K) and orbits an A0V-type star. Studies of the upper atmosphere and escaping gas of this u…
A 3D fully self-consistent multi-fluid hydrodynamic aeronomy model is applied to simulate the hydrogen-helium expanding upper atmosphere of the hot Jupiter HD189733b, and related absorption in the Lya line and the 10830 A line of metastable helium. We studied the influence of a high-energy stellar flux, stellar wind, and Lya cooling to reproduce the available observations. We found that to fit the width of the absorption profile in 10830 A line the escaping upper atmosphere of planet should be close to the energy limited escape achieved with a significantly reduced Lya cooling at the altitudes…
Hydrogen airglow from an escaping ultrahot Jupiter atmosphere
California Institute of Technology（加州理工学院）；Shanghai Astronomical Observatory, Chinese Academy of Sciences（中国科学院上海天文台）；Massachusetts Institute of Technology（麻省理工学院）；Imperial College London（伦敦帝国学院）；University of Hawaii at Mānoa（夏威夷大学马诺阿分校）；University of California Berkeley（加州大学伯克利分校）
A Search for helium in the atmospheres of three sub-Neptunes and a super-Earth around M-dwarfs
Department of Physical Sciences, Ritsumeikan University（立命馆大学物理科学系）；Komaba Institute for Science, The University of Tokyo（东京大学驹场科学研究所）；Instituto de Astrofísica de Canarias (IAC)（加那利天体物理研究所）；Astrobiology Center（天体生物学中心）；National Astronomical Observatory of Japan（日本国立天文台）；Department of Physics, College of Science, Rikkyo University（立教大学理学部物理学科）；Department of Astronomical Science, The Graduate University for Advanced Studies (SOKENDAI)（高级研究院天文学科学系）
Escaping atmosphere has been detected by the excess absorption of Ly$α$, H$α$ and He triplet (10830$\rmÅ$) lines. Simultaneously modeling the absorption of the H$α$ and He 10830 lines can provide useful constraints about the exoplanetary atmosphere. In this paper, we use a hydrodynamic model combined with a non-local thermodynamic model and a new Monte Carlo simulation model to obtain the H(2) and He(2$^3$S) populations. The Monte Carlo simulations of Ly$α$ radiative transfer are performed with assumptions of a spherical stellar Ly$α$ radiation and a spherical planetary atmosphere, for the fir…
We detect Lyman $α$ absorption from the escaping atmosphere of HD 63433c, a $R=2.67 R_\oplus$, $P=20.5$ d mini Neptune orbiting a young (440 Myr) solar analogue in the Ursa Major Moving Group. Using HST/STIS, we measure a transit depth of $11.1 \pm 1.5$% in the blue wing and $8 \pm 3$% in the red. This signal is unlikely to be due to stellar variability, but should be confirmed by an upcoming second visit with HST. We do not detect Lyman $α$ absorption from the inner planet, a smaller $R=2.15 R_\oplus$ mini Neptune on a 7.1 d orbit. We use Keck/NIRSPEC to place an upper limit of 0.5% on helium…
Exoplanets orbiting very close to their host star are strongly irradiated. This can lead the upper atmospheric layers to expand and evaporate into space. The metastable helium (HeI) triplet at 1083.3nm has recently been shown to be a powerful diagnostic to probe extended and escaping exoplanetary atmosphere. We perform high-resolution transmission spectroscopy of the transiting hot Jupiter HD189733b with the GIARPS (GIANO-B + HARPS-N) observing mode of the Telescopio Nazionale Galileo, taking advantage of the simultaneous optical+near infrared spectral coverage to detect HeI in the planet's ex…
We explore atmospheric escape from close-in exoplanets with the highest mass loss rates. First, we locate the transition from stellar X-ray and UV-driven escape to rapid Roche lobe overflow, which occurs once the 10-100 nbar pressure level in the atmosphere reaches the Roche lobe. Planets enter this regime when the ratio of the substellar radius to the polar radius along the visible surface pressure level, that aligns with a surface of constant Roche potential, is X/Z~$\gtrsim$~1.2 for Jovian planets (Mp~$\gtrsim$~100 M$_{\Earth}$) and X/Z~$\gtrsim$~1.02 for sub-Jovian planets ($M_p \approx$~1…
Aims: We aim at constraining the conditions of the wind and high-energy emission of the host star reproducing the non-detection of Ly$α$ planetary absorption. Methods: We model the escaping planetary atmosphere, the stellar wind, and their interaction employing a multi-fluid, three-dimensional hydrodynamic code. We assume a planetary atmosphere composed of hydrogen and helium. We run models varying the stellar high-energy emission and stellar mass-loss rate, further computing for each case the Ly$α$ synthetic planetary atmospheric absorption and comparing it with the observations. Results: We …
Atmospheric escape is considered to be one of the main channels for evolution in sub-Jovian planets, particularly in their early lives. While there are several hypotheses proposed to explain escape in exoplanets, testing them with atmospheric observations remains a challenge. In this context, high-resolution transmission spectroscopy of transiting exoplanets for the metastable helium triplet (He 2$^3$S) at $1\,083$ nm has emerged as a reliable technique to observe and measure escape. To aid in the prediction and interpretation of metastable He transmission spectroscopy observations, we develop…
