Akatsuki Mission Update: New Images and Status of the Mission Mark A. Bullock Southwest Research Institute Sep 13, 2016 Venus Winds Meeting, DMNS

New Image from 2 micron Camera Thermal radiation from the night side at 2.26 microns – the same as our IRTF images Taken on April 26, 2016 from a distance of 76,000 km Scattered sunlight from dayside is a serious problem Multiple ghost images due to anomalous electronics read-out noise also a problem

2 micron Image of Venus’ Day Side Unlike the previous image, this image is of the day side – reflected sunlight at 2.02 microns CO2 absorbs at this wavelength, so variations in brightness are due to differences in the height of the cloud tops Darker regions are where cloud tops are lower because there is more CO2 for the sunlight to go through Taken May 6, 2016 at a distance of 81,000 km

UV Image of Venus in Reflected Sunlight Taken in reflected UV sunlight at 283 nm Sunlight is absorbed by SO2 in the atmosphere above the clouds Variations in brightness due to variations in SO2 abundance Taken on April 25, 2016 from a distance of 108,000 km

UV Image of Venus in Reflected Sunlight Taken in reflected UV sunlight at 365 nm Sunlight is absorbed by SO2 in the atmosphere above the clouds Variations in brightness due to variations in SO2 abundance Taken on May 6, 2016 from a distance of 80,000 km

Night Side Image of Venus’ Surface* This is the thermal radiation from the hot surface 1 micron camera looks through the 1.02 micron window all the way to the surface Dark regions are cooler because they are higher Taken on Jan 21, 2016 at a distance of 38,000 km *Sort of. Varying cloud thickness is superimposed on the surface image

Comparison of Surface Image with Topography

Day Side of Venus in 0.90 mm Reflected Sunlight Similar wavelength as previous image, but in reflected sunlight, not thermal emission from the surface Shows subtle features just below cloud tops Much brighter than night side image – shorter exposure Taken on May 6, 2016 from a distance of 65,000 km

Cloud Top Temperature Image Taken with the Long Wavelength Infrared (LIR) camera at 10 microns Maps the temperature at the cloud tops Bow shaped feature seen earlier is absent (see next slide) Taken on April 15, 2016 from a distance of 63,000 km

Changes in Cloud Top Features December 7, 2015 April 15, 2016 The bow-like feature seems to return every 2 Venus days (2 x 225 days)

Movie Clip of Cloud Motion 4 frames of Venus’ nightside at 2.26 mm Each frame is 4 hours apart Clouds rotate a total of 10° Taken on March 29, 2016 from a distance of 360,000 km

My Akatsuki Project Goal: Look for signs of active volcanism using images of the surface and correlations with changes in the atmosphere and clouds Compare Akatsuki ‘surface’ images with those taken by Venus Express 10 years before Make 3-color surface images with 0.90, 0.97 and 1.02 mm images to look for composition differences due to volcanism or weathering Use IRTF spectra to map atmospheric SO2 and H2O below the clouds

Possible (speculative) Evidence for Volcanism Smrekar et al. 2010 Idunn Mons VIRTIS emissivity overlain on Magellan radar image of volcano High emissivity: Dark, unweathered lava flows? Stofan et al. 2005 found 3 possible young volcanic centers in southern hemisphere, 6 in northern hemisphere

1.02 mm Surface Emissivity from VIRTIS From Mueller et al. 2008. Southern Hemisphere only Akatsuki can see the whole planet, and emissivity at 3 wavelengths

IRTF/SpeX Image Cubes 2001-2015

Mapping Sub-Cloud Atmospheric Abundances 25 Nov 27 Nov 30 Nov 2 Dec 3 Dec 4 Dec 2010 Co-added 3.5 m Apache Point observations and retrievals by Arney et al. 2014 R = 3500.

3 Color Surface Emissivities From Baines et al. (2000) Galileo NIMS Very strong differences in slopes across 0.9, 0.97, 1.02 mm for different minerals. However, mineral emissivity at high T,P of Venus surface will be very different from this