Science‎ > ‎

Titan

Hazes dramatically influence exoplanet observations by obscuring deeper atmospheric layers.  This effect is especially pronounced in transit spectroscopy, which 
probes an exoplanet's atmosphere as it crosses the disk of its host star.  However, exoplanet observations are typically noisy, which hinders our ability to disentangle haze effects from other processes.  In a recent paper, we turned to Titan, an extremely well-studied world with a hazy atmosphere, to better understand how high altitude hazes can impact exoplanet transit observations.  We solar occultation observations from the Visual and Infrared Mapping Spectrometer (VIMS) instrument aboard NASA's Cassini spacecraft to effectively view Titan in transit.  These new data challenge our understanding of how hazes influence exoplanet transit observations, and provide a means of testing proposed approaches for exoplanet characterization.

The GIF below demonstrates the appearance of a model solar disk setting through Titan's atmosphere at four different wavelengths.  Using the full spectral range observed by VIMS (0.88-5 μm), we generated the transit spectra shown below.  Here, the four curves correspond to the different occultation datasets that we used.  The data for these transit radius spectra are available here.  If you use these, please cite the aforementioned paper.

                                                            1.0 μm           2.9 μm           3.4 μm           4.5 μm

This movie shows model images of the Sun setting through Titan's atmosphere at different wavelengths.  Altitude (in km) is shown at left.  Moving from left to right, the wavelengths are: 
1.0 μm (continuum wavelength where haze absorbs strongly), 2.9 μm (continuum wavelength where haze absorbs moderately), 3.4 μm (center of a strong methane band), and 4.5 μm (weak haze and carbon monoxide absorption).


Spectra of effective transit height, zeff, for four Cassini/VIMS occultation datasets. Note that the transit depth signal is proportional to (zeff + Rp)2, where Rp is the planetary radius (i.e., 2575 km for Titan).  Key absorption features are labeled, and error bars are shown only where the 1-σ uncertainty is larger than 1%.