Over the past decade, observations of giant exoplanets (Jupiter-size) have provided key insights into their atmospheres, but the properties of lower-mass exoplanets (sub-Neptune) remain largely unconstrained because of the challenges of observing small planets. Numerous efforts to observe the spectra of super-Earths--exoplanets with masses of one to ten times that of Earth--have so far revealed only featureless spectra. Here we report a longitudinal thermal brightness map of the nearby transiting super-Earth 55 Cancri e (refs 4, 5) revealing highly asymmetric dayside thermal emission and a strong day-night temperature contrast. Dedicated space-based monitoring of the planet in the infrared revealed a modulation of the thermal flux as 55 Cancri e revolves around its star in a tidally locked configuration. These observations reveal a hot spot that is located 41 ± 12 degrees east of the substellar point (the point at which incident light from the star is perpendicular to the surface of the planet). From the orbital phase curve, we also constrain the nightside brightness temperature of the planet to 1,380 ± 400 kelvin and the temperature of the warmest hemisphere (centred on the hot spot) to be about 1,300 kelvin hotter (2,700 ± 270 kelvin) at a wavelength of 4.5 micrometres, which indicates inefficient heat redistribution from the dayside to the nightside. Our observations are consistent with either an optically thick atmosphere with heat recirculation confined to the planetary dayside, or a planet devoid of atmosphere with low-viscosity magma flows at the surface.

Seven temperate Earth-sized exoplanets readily amenable for atmospheric studies transit the nearby ultra-cool dwarf star TRAPPIST-1 1, 2 . Their atmospheric regime is unknown and could range from extended primordial hydrogen-dominated to depleted atmospheres 3-6 .Hydrogen in particular is a powerful greenhouse gas that may prevent the habitability of inner planets while enabling the habitability of outer ones [6][7][8] . An atmosphere largely dominated by hydrogen, if cloud-free, should yield prominent spectroscopic signatures in 2 the near-infrared detectable during transits. Observations of the innermost planets ruled out such signatures 9 . However, the outermost planets are more likely to have sustained such a Neptune-like atmosphere 10,11 . Here, we report observations for the four planets within or near the system's "Habitable Zone" (HZ)-the circumstellar region where liquid water could exist on a planetary surface 12-14 . These planets do not exhibit prominent spectroscopic signatures at near-infrared wavelengths either, which rules out cloud-free hydrogen-dominated atmospheres for TRAPPIST-1 d, e and f with significance of 8, 6 and 4σ, respectively. Such an atmosphere is instead not excluded for planet g. As highaltitude clouds and hazes are not expected in hydrogen-dominated atmospheres around planets with such insolation 15,16 , these observations further support their terrestrial and potentially habitable nature.We observed transits of TRAPPIST-1 planets d, e, f, and g with four visits of the Hubble Space Telescope (HST). Each of the visits contained two planetary transits (Figure 1), planets d and f in visits 1 (4 December 2016) and 3 (9 January 2017), and planets e and g in visits 2 (29 December 2016) and 4 (10 January 2017). The observations were conducted using the 'forward' scanning mode with the near-infrared (1.1-1.7µm) G141 grism on the wide-field camera 3 (WFC3) instrument (see Methods). We capitalized on the frequency of the transit events in the TRAPPIST-1 system to select observation windows encompassing transits from two different planets, thereby optimizing the time allocation. The time sensitivity of these observations (TRAPPIST-1's visibility window closing in January 2017) combined with our 3 "multiple-transit-per-visit" approach constrained us to perform exposures when HST crossed through the South-Atlantic Anomaly (SAA). Visits 1, 3, and 4 contain SAA crossing events which forces HST into GYRO mode, where its fine pointing ability is lost. The loss of fine pointing during and following the SAA crossing events cause the spectral position on the detector to change over time. In addition, during the SAA crossing a greater number of cosmic ray hits are introduced to the observations/exposures. We use the IMA output files from the CalWF3 pipeline and correct for this by cross-correlating each spectral read in the individual exposures and interpolating (see Methods). The raw light curves present primarily ramp-like systematics on the scale of HST orbit-induced instrumental settling discuss...

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