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

2. 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

3. 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

4. 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

5. 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

6. 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

7. Comparison of Surface Image with Topography

8. 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

9. 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

10. 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)

11. 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

12. 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

13. 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 found 3 possible young volcanic centers in southern hemisphere, 6 in northern hemisphere

14. 1.02 mm Surface Emissivity from VIRTIS
From Mueller et al
Southern Hemisphere only
Akatsuki can see the whole planet, and emissivity at 3 wavelengths

15. IRTF/SpeX Image Cubes 2001-2015

16. Mapping Sub-Cloud Atmospheric Abundances
25 Nov Nov Nov Dec Dec Dec Co-added
3.5 m Apache Point observations and retrievals by Arney et al R = 3500.

17. 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