Hubble Science Briefing 23 Years of Exoplanets with the Hubble Space Telescope Dr. John H. Debes, Dr. Remi Soummer, & Dr. Nikole K. Lewis October 26th, 2015

Hubble’s Studies of Planet Formation and Evolution in Dusty Disks around Stars Dr. John Debes

HST Is Pivotal in Exoplanet Science Resolution Space Hubble has essentially been pivotal in the field of exoplanets for many of the same reasons Hubble is pivotal in many fields 1) No atmosphere 2) Resolution 3) Precision We’ll talk about each of these things implicitly in each of the following sections. Precision

A Stellar Nursery Laid Bare Proplyds—the first disks observed with Hubble that are in the process of forming planets. First images were from 1992. Earliest exoplanet system observation with a press release from STScI was of Beta Pictoris in 1991 with Goddard High Resolution Spectrometer.

First Peeks at Protoplanetary Disks (left) The HH 30 protoplanetary disk. The disk appears as a dark lane that bisects the scattered light from the disk surface. A jet (green in this false color image) shows that this star is actively accreting material at a high rate. (right) HH 30 over time, showing that on short timescales, the jet precesses. STScI-1999-05 STScI-2000-32

Complex Structures Hint at Planet Formation Ardila et al., 2007 STScI-2013-20

The Late Stages of Planet Formation STScI-2006-25 STScI-1998-03 Macintosh, et al., 2014

The Late Stages of Planet Formation STScI-2014-44

Chemistry in Disks Roberge et al., 2006

Chemistry in Disks HST-2013-18 Xu et al., 2014

Hubble’s Direct Detections of Exoplanets Dr. Rémi Soummer

Direct Imaging of Exoplanets Mercury and Venus visible during solar eclipse The goal is to reproduce this effect for another star, using optical instrumentation

Case of a perfect telescope Diffraction pattern of a star with perfect telescope

Case of a perfect telescope Diffraction pattern of a star with perfect telescope, increasing the scaling

Case of a perfect telescope Diffraction pattern of a star with perfect telescope, increasing the scaling

Case of a perfect telescope

Starlight suppression with coronagraph

Reference star subtraction Courtesy M. Perrin

Fomalhaut b HST Observations Kalas et al. (2008+)

HD 106906b Large separation 11 Jupiter mass companion discovered using ground-based observations Bailey et al. 2014 An exoplanet 11 times the mass of Jupiter was directly observed around the young, 13 million year old star HD 106906. The companion exoplanet is orbiting around a massive debris disk that surrounds the parent star. The companion has a large separation from the parent star - 7 arcseconds away. Could it just be a chance alignment in the sky of two disconnected objects? Hubble archival data was used to confirm that the parent star and companion have a common proper motion - i.e. they are traveling together through space, hinting at their connection. Common Proper Motion was confirmed by HST archival data from several years ago i.e. it is not a chance alignment with background object

HR 8799 in 1998 HST archival data These results were made possible by post-processing speckle subtraction and achieve over an order of magnitude contrast improvement over the state of the art when the data was taken in 1998. Contrast of these images are in the range 104 to 105 to 1

Reference star subtraction

Temporal evolution of HST Optical Telescope Assembly (OTA)

Improved subtraction

New images of debris disks

Probing Exoplanet Atmospheres with Hubble Dr. Nikole Lewis

Confirmed Exoplanet Population Current population of confirmed exoplanets. The population of exoplanets that transit their host star largely occupy orbital periods shorter than that of Mercury in our own solar system. Since most transiting exoplanets orbit closely to their host star, they can be assumed to be tidally locked (rotation period = orbital period), like the moon is to Earth.

Transiting Exoplanets When an exoplanet transits its host star as seen from earth, its atmosphere can be probed using various techniques Figure credit: Prof. Sara Seager

Transiting Exoplanets This what transit observations look like schematically. The largest signal occurs when the planet passes in front of its host star as seen from earth. A second dip in the flux from the system occurs as the planet passes behind its host star as seen from earth. Flux from the planet is present at all orbital phase. Assuming that a planet is tidally locked, these ‘phase-variations’ can be used to map a planet’s atmosphere. Figure credit: Winn (2011)

Transiting Exoplanets with HST The Hubble Space Telescope has been used to probe exoplanets atmospheres at wavelengths from the infrared to the UV.

Detection of Sodium Figure credit: Paul A. Wilson Sodium has a large spectral feature in the visible that theorists predicted should be readily visible in transmission (transit) spectra of exoplanets. Figure credit: Paul A. Wilson

Detection of Sodium HD 209458b STIS Observations Charbonneau et al. (2001) Soon after the discovery of the first transiting exoplanet in 2000, Hubble was used to measure the Sodium spectral feature in the atmosphere of HD 209458b. First Detection of an Exoplanet Atmosphere!

Detection of Molecules HD 189733b NICMOS Observations Swain et al. (2008) Observations with Hubble’s NICMOS (near-infrared wavelengths) instrument of the transmission spectrum of HD 189733b revealed the presence of Methane and Water in the planet’s atmosphere. The first detection of molecules in the atmospheres of exoplanets. First Detection of Molecules in Exoplanet Atmosphere!

Detection of Haze HD 189733b STIS Observations Sing et al. (2011) Observations of exoplanet HD 189733b using Hubble’s STIS instrument (visible wavelengths) in transmission revealed that the expected Sodium (Na) and Potassium (K) features were not present in this planet. Instead the data suggests the presence of a haze/cloud layer in the planet’s atmosphere.

Water in Exoplanets WFC3 Observations Madhusudhan et al. (2011) Since the installation of the WFC3 instrument on Hubble in 2009, it has been a workhorse for transiting exoplanet science. The Near-Infrared wavelength range of WFC3 probes important Water spectral features that would be obscured by own atmospheric water if the instrument were on a ground-based telescope. The water features in ‘hot Jupiters’ are weaker than expected, indicating either a dry atmosphere or the presence of clouds/hazes that suppress the strength of the spectral features. Image Credit: NASA, ESA, University of Cambridge, and STScI

Probing a Super-Earth Hubble has also been used to probe the atmosphere of an entirely new class of planets called ‘Super-Earths’. These planets have a size intermediary to the size of Earth and Neptune and have no Solar System analogues. Given their size, it is possible that they host a wide range of atmospheric compositions. Early observations revealed a ‘flat’ transmission spectrum that suggest either an atmosphere that was tightly bound to the planet and composed of high molecular weight elements/molecules or a planet that had a thick cloud layer.

Probing a Super-Earth GJ 1214 b WFC3 Observations Kreidberg et al. (2014) Observations using Hubble’s WFC3 found that the atmosphere of GJ1214b must possess a thick cloud layer. The high molecular weight scenario is excluded by comparing the data with models of atmosphere dominated by water, carbon dioxide, or methane.

Mapping Exoplanets Credit: NASA, ESA, and Z. Levay (STScI) Hubble has also been used to probe the thermal emission from exoplanets as a function of orbital phase. Most transiting exoplanets can be assumed to be tidally locked (like the moon) and present different phases as they orbit around their host star. Credit: NASA, ESA, and Z. Levay (STScI)

Mapping Exoplanets WASP-43b WFC3 Observations Stevenson et al. (2014) Phase-curve observations using Hubble’s WFC3 were used to measure the variation in infrared flux from the planet WASP-43b as a function of orbital phase. Such observations allow us to create maps of the planet as a function of longitude and detect the presence of winds. WASP-43b WFC3 Observations Stevenson et al. (2014)

Mapping Exoplanets WASP-43b GCM Model Kataria et al. (2015) Phase curve observations are useful for testing general circulation models of exoplanet atmospheres. Most general circulation model predict that the peak temperatures of the planet will be displaced to the east of the substellar point (solid line) due to the presence of winds that are on the order of 1 km/s. Observational predictions from these general circulation models well match phase-curve observations of planets like WASP-43b. WASP-43b GCM Model Kataria et al. (2015)

Evaporating Exoplanet Atmospheres GJ 436b Transit observations of the Neptune-sized planet GJ 436b in the ultraviolet probed the extended hydrogen envelope of the planet. These Hubble STIS observations revealed an asymmetry in the transit shape that indicate a cometary-like tail for the planet formed by hydrogen gas escaping from the planet’s atmosphere. STIS UV Observations Enrenreich et al. (2015) Image Credit: NASA/ESA/STScI

The James Webb Space Telescope (JWST) JWST will dramatically enhance our understanding of star & planet formation and probe the atmospheres of nearby small rocky exoplanets to search for habitability.