Transiting hot Uranus at GJ 3470

A hot Uranus transiting the nearby M dwarf GJ3470. Detected with HARPS velocimetry. Captured in transit with TRAPPIST photometry
http://arxiv.org/abs/1206.5307

Quote :

We report on the discovery of GJ3470b, a transiting hot Uranus of mass m_p = 14.0+-1.8 Mearth, radius R_p = 4.2+-0.6 Rearth and period P=3.3371+-0.0002 day. Its host star is a nearby (d=25.2+-2.9pc) M1.5 dwarf of mass M_s=0.54+-0.07 Msol and radius R_s=0.50+-0.06 Rsol. The detection originates from a radial-velocity campaign with HARPS that focused on the search for short-period planets orbiting M dwarfs. Once the planet was discovered and the transit-search window narrowed to about 10% of an orbital period, a photometric search started with TRAPPIST and quickly detected the ingress of the planet. Additional observations with TRAPPIST, EulerCam and NITES definitely confirmed the transiting nature of GJ3470b and allow for the determination of its true mass and radius. The star's visible or infrared brightness (V=12.3, K=8.0 mag), together with a large eclipse depth D=0.57+-0.05%, ranks GJ3470b among the most favorable planets for follow-up characterizations.

Nice find quite close.Planets max equilibrum temp is 615 K so no significant mass loss had place

Pity the assignment of this star as a member of the Hyades supercluster appears to be incorrect, would be interesting to have another cluster planet.

How would a hot Uranus differ from a hot Neptune? I know that sounds like a dumb question...would it appear different?

-M-

In appearance or density(composition) you ask?

Mass?

Appearance. In the paper they have a density of approximately 1.07 g/cm3. Are they comparing it to Uranus because of the similar mass and density?

-M-

I'm almost sure it's just mass. A Neptune that is just under 1 M_Neptune you might call a Uranus. Neptune has a mass of 17 M_E, Uranus has a mass of 14 M_E. GJ 3470 b's mass is clearly more similar to that of Uranus. That seems to be the only significant difference (temperature aside!). The planet's mass, radius and density are effectively indistinguishable from that of Uranus (the values for those of Uranus fall within the error margin of those of GJ 3470 b).

...and maybe because they are from countries which have languages other than English they aren't so concerned about that stupid joke.

I suspect that may be why we have the term sub-Neptunes rather than sub-Uranuses (and maybe the awkward plural).

Or because Neptune is the more massive/dominant of the ice giants (cf. Jupiter vs. Saturn, Earth vs. Venus)?

Update: GJ 3470b is less dense than previously thought, may be an analogue for the Kepler-11 planets.

Spitzer Observations of GJ3470b: a Very Low-density Neptune-size Planet Orbiting a Metal-rich M dwarf
http://arxiv.org/abs/1301.6555

Even with larger radius due to assessing larger stellar radius planet R 4.83 is bigger than 4.5 for Kepler 11 e but 25% denser ,the same as k11 f despite almost twice larger R.It sseems to be that kepler 11 planets d,e,f,and maybe g are the least dense of all super earth - Neptune range excluding planets with significant mass loss.Examples kepler 20c,gj 1214b,kepler30b,corot 24 c

An apparently cloudless atmosphere could make this planet an awesome transmission spectroscopy follow-up target.

Optical-to-Near-Infrared Simultaneous Observations for the Hot Uranus GJ3470b: A Hint for Cloud-free Atmosphere
http://arxiv.org/abs/1302.7257

Warm Ice Giant GJ 3470b. I. A Flat Transmission Spectrum Indicates a Hazy, Low-methane, and/or Metal-rich Atmosphere
http://arxiv.org/abs/1308.6580

Quote :

Thus, if the atmosphere is cloud-free its spectral features should be detectable with future observations. Transit observations at shorter wavelengths will provide the best opportunity to discriminate between plausible scenarios

And on arXiv tonight are observations just like that.

The blue sky of GJ3470b: the atmosphere of a low-mass planet unveiled by ground-based photometry
http://arxiv.org/abs/1308.6765

Quote :

Simultaneous photometry in the ultraviolet (lambda_c = 357.5 nm) and optical infrared (lambda_c = 963.5 nm) allowed us to detect a significant change of the effective radius of GJ3470b as a function of wavelength. This can be interpreted as a signature of scattering processes occurring in the planetary atmosphere, which should be cloud-free and with a low mean molecular weight.

other blue planet?

So, it is not clear if the transmission spectrum is flat or not. Both papers seems to be not compatible, isn' t it? What a mess.

Well, making measurements of the atmospheres of planets orbiting stars many light years away is pretty difficult. Who would have guessed?

pochimax wrote:

Both papers seems to be not compatible, isn't it?

Well… not really. The two papers observe different wavelengths of the emission spectrum, with Nascimbeni et al. observing shorter wavelengths than Crossfield et al. Because of that, Crossfield et al.'s data are consistent with a flat spectrum because they are observing part of it where the changes in transit depth are slight, whereas Nascimbeni et al. detect significant variation in transit depth as they observe part of the spectrum which shows considerably larger variation.

Near-infrared transmission spectrum of the warm-uranus GJ 3470b with the Wide Field Camera-3 on the Hubble Space Telescope
http://arxiv.org/abs/1405.1056

Quote :

The atmospheric composition of low-mass exoplanets is the object of intense observational and theoretical investigations. GJ3470b is a warm uranus recently detected in transit across a bright late-type star. The transit of this planet has already been observed in several band passes from the ground and space, allowing observers to draw an intriguing yet incomplete transmission spectrum of the planet atmospheric limb. In particular, published data in the visible suggest the existence of a Rayleigh scattering slope, making GJ3470b a unique case among the known neptunes, while data obtained beyond 2 um are consistent with a flat infrared spectrum. The unexplored near-infrared spectral region between 1 and 2 um, is thus key to undertanding the atmospheric nature of GJ3470b. Here, we report on the first space-borne spectrum of GJ3470, obtained during one transit of the planet with WFC3 on board HST, operated in stare mode. The spectrum covers the 1.1--1.7-um region with a resolution of about 300. We retrieve the transmission spectrum of GJ3470b with a chromatic planet-to-star radius ratio precision of 0.15% (about one scale height) per 40-nm bins. At this precision, the spectrum appears featureless, in good agreement with ground-based and Spitzer infrared data at longer wavelengths, pointing to a flat transmission spectrum from 1 to 5 um. We present new simulations of transmission spectra for GJ3470b, which allow us to show that the HST/WFC3 observations rule out cloudless hydrogen-rich atmospheres (>10 sigma) as well as hydrogen-rich atmospheres with tholin haze (>5 sigma). Adding our near-infrared measurements to the full set of previously published data from 0.3 to 5 um, we find that a cloudy, hydrogen-rich atmosphere can explain the full transmission spectrum if, at the terminator, the clouds are located at low pressures (<1 mbar) or the water mixing ratio is extremely low (<1 ppm).

Warm Ice Giant GJ 3470b. II Revised Planetary and Stellar Parameters from Optical to Near-infrared Transit Photometry
http://arxiv.org/abs/1406.6437

Looks like the data supports an H₂-dominated atmosphere.

Big difference of planet radius 4.83 earth to 3.88??  

It's evaporating!

Hubble PanCET: an extended upper atmosphere of neutral hydrogen around the warm Neptune GJ 3470b
https://www.aanda.org/articles/aa/abs/2018/12/aa33675-18/aa33675-18.html

Physorg.
https://phys.org/news/2018-12-hubble-far-away-planet.html

Quote :

In their quest to learn more about far-away planets beyond our own solar system, astronomers discovered that a medium-sized planet roughly the size of Neptune, GJ 3470b, is evaporating at a rate 100 times faster than a previously discovered planet of similar size, GJ 436b.

Quote :

"This is the smoking gun that planets can lose a significant fraction of their entire mass. GJ 3470b is losing more of its mass than any other planet we seen so far; in only a few billion years from now, half of the planet may be gone," said David Sing, Bloomberg Distinguished Professor at Johns Hopkins and an author on the study.

A Sub-Neptune Exoplanet with a Low-Metallicity Methane-Depleted Atmosphere and Mie-Scattering Clouds
https://arxiv.org/abs/1907.00449

Quote :

With no analogues in the Solar System, the discovery of thousands of exoplanets with masses and radii intermediate between Earth and Neptune was one of the big surprises of exoplanet science. These super-Earths and sub-Neptunes likely represent the most common outcome of planet formation. Mass and radius measurements indicate a diversity in bulk composition much wider than for gas giants; however, direct spectroscopic detections of molecular absorption and constraints on the gas mixing ratios have largely remained limited to planets more massive than Neptune. Here, we analyze a combined Hubble/Spitzer Space Telescope dataset of 12 transits and 20 eclipses of the sub-Neptune GJ 3470 b, whose mass of 12.6 M⊕ places it near the half-way point between previously studied exo-Neptunes (22-23 M⊕) and exoplanets known to have rocky densities (7 M⊕). Obtained over many years, our data set provides a robust detection of water absorption (>5σ) and a thermal emission detection from the lowest irradiated planet to date. We reveal a low-metallicity, hydrogen-dominated atmosphere similar to a gas giant, but strongly depleted in methane gas. The low, near-solar metallicity (O/H=0.2-18) sets important constraints on the potential planet formation processes at low masses as well as the subsequent accretion of solids. The low methane abundance indicates that methane is destroyed much more efficiently than previously predicted, suggesting that the CH4/CO transition curve has to be revisited for close-in planets. Finally, we also find a sharp drop in the cloud opacity at 2-3 μm characteristic of Mie scattering, which enables narrow constraints on the cloud particle size and makes GJ 3470b a keystone target for mid-IR characterization with JWST.

Press release.

Atmosphere of Mid-Size Planet Revealed by Hubble and Spitzer
https://www.nasa.gov/feature/goddard/2019/atmosphere-of-mid-size-planet-revealed-by-hubble-and-spitzer