1. Observing Venus (and Mars) with Adaptive Optics
Jeremy Bailey (UNSW)

2. Adaptive Optics
Many large ground-based telescopes are equipped with adaptive optics.
These allow diffraction limited imaging at near-IR wavelengths.
At 2 mm diffraction limit of a telescope is:
But currently we are limited by seeing to resolutiond of 0.5–1.0 arcsec ( km). B
Aperture
Arc sec
Km at Venus/Mars
4 m
0.13 32
8 m
0.07 16
32 m
0.016 4

3. Extremely Large Telescopes
Even larger telescopes – known as Extremely Large telescopes (or ELTs) are now being designed.
Thirty Metre Telescope (TMT)

4. Adaptive Optics images
Titan with ESO VLT
Jupiter with Gemini Telescope and adaptive optics — image processed by Chris Go.
Uranus and its rings with Keck telescope

5. Titan
Gemini AO Images
NIFS Images

6. Current AO Systems Require a guide “star” close to the science object.
With a planet like Mars or Venus …
Too big to be used as a guide star itself.
Too bright to allow a nearby star to be used as a guide star (scattered light).
e.g. Attempts to use Phobos (mag 10.4) as a guide star for Mars (mag -2.8) have not been successful.
Laser guide stars don’t help.

7. VEX VIRTIS-M
R ~ 200
AAT IRIS2
R ~ 2400

8. Resolution at Mars/Venus
(Near-IR Imaging Spectrometers)

9. Resolution at Mars/Venus
(Near-IR Imaging Spectrometers)

10. Limb viewing
The resolution of GMTIFS at Mars and Venus (~3-4km) is sufficient to vertically resolve the atmosphere in limb viewing geometry.
Spacecraft can do this, but it has never before been possible with ground-based telescopes.

11. Current Performance - UKIRT 90km resolution
MGS MOLA data

12. 8m Telescope - Diffraction
Limited at 2mm - 16km resolution

13. ELT
4km resolution

14. Solution
We need an AO wavefront sensor that can work on the extended structure of the image of Mars or Venus (rather than a point source).
For Venus use the 2.3 mm cloud structure or 1.27 mm airglow (or perhaps the sunlit crescent in the visible).
For Mars use the surface albedo features.
We know this is possible because solar AO systems work on extended structure (e.g. solar granulation).

15. Shack-Hartmann Wavefront Sensor

16. Correlating Shack-Hartmann
Used in solar adaptive optics systems.
Measures image shifts by correlating structure in individual pupil images.
Intel processors contain specific support for rapid measurements of image shifts in their SSE instruction sets (as it is important for video compression algorithms)

17. Solar AO Example
Data taken with “low cost” AO system for McMath Pierce solar telescope.
Hardware cost US$25,000
Keller et al., 2003, SPIE Proc. 4853, 351.

18. Options Build a new instrument designed for planetary AO.
Retrofit “correlating” capability to an existing AO system.
Use a solar telescope (that already has this capability) to observe Venus.
Shoud work very well – these planets are bright sources and should be capable of provding good (high Strehl) AO correction.