Science Concept Information Sheet
Break-out:
Venus
Form completed by: Eliot Young
Concept title (ID): Venus Night Cloud Circulation (14)
Description of the potential science / science goals:
Observe Venus' lower and middle cloud decks (~45 - 55 km) in CO2 windows at 1.74 and 2.25 - 2.55 µm,
where these clouds show up as silhouettes against thermal flux emitted from Venus' surface and lower
two scale heights. These observations enable cloud tracking studies (as proxies for wind vectors),
identification of cloud properties (cloud acidities, sizes of aerosols and rough estimates of height) and
mapping of several trace gases (such as CO, OCS, H2O and SO2).
Relevance of the science (Why is this important?) What are the specific Decadal ties?
Addresses several questions raised in the Decadal Survey (see p. 121):
(1) How do clouds influence radiative balance in Venus' atmosphere?
(2) How does Venus' global circulation differ from that of Earth and Mars?
(3) What are the key processes, reactions and chemical cycles controlling the chemistry of the lowermiddle-upper atmosphere of Venus?
What measurements are required to achieve the science?
Imaging of Venus in about 10 - 20 narrow band filters near 1.74 µm and between 2.25 - 2.55 µm,
corresponding to CO2 windows.
What are the driving requirements to achieve the measurements? (E.g. time on target, frequency of
observations, aperture, focal length, wavelengths, pointing precision and stability, specific observing
location(s), critical observation time(s), are repeat flights required? or whatever else that may drive the
hardware or mission design/architecture).
Telescope aperture:
2m
2m class is required to achieve 0.22" resolution imaging at 1.74 µm, equivalent to about 44 km on Venus
at inferior conjunction. A balloon-borne platform, tracking cloud features for several (5+) hours
continuously, could track cloud features at the sub- 1 m/s level, sufficient to characterize meridional
motion and possibly sufficient to characterize angular momentum transport by comparing
instantaneous to average u and v velocities.
Telescope focal length: about 40m
Wavelengths: 1.74 - 2.55 µm
Pointing precision: 0.1".
Required time on target: 20 -40 days. Images in all filters can be obtained in tens of minutes, but a
baseline of several hours is necessary to get reliable cloud motion rates. Total mission durations of 20 to
40 days (centered on inferior conjunction) are necessary to look for planetary wave phenomena that are
predicted in GCMs.
Are there other ways to achieve this science, and if so, why would a balloon platform be preferable?
The JAXA/VCO mission would have provided images of Venus at 1.74, 2.30 and 2.32 µm that would have
provided excellent cloud tracking and CO mapping data sets, but VCO did not enter orbit around Venus.
Venus Express VIRTIR IR image cubes (no longer obtainable) provided repeated cloud tracking rates of
the southern hemisphere at the 5 m/s level. IRTF observations provided rates of the N and S
hemispheres at the 3.5 m/s level in the best seeing conditions. A balloon mission is necessary for three
reasons: (1) long, uninterrupted observing baselines of several hours are essential to determine cloud
motions at the 1 m/s level and better, (2) a mission duration of 20 - 40 continuous days is necessary to
characterize planetary wave phenomena, and (3) certain wavelengths are opaque at the Earth's surface
(e.g., 2.53 µm, important for establishing cloud altitudes, is difficult to observe from ground-based
telescopes).
What are the potential observation targets?
Venus during inferior conjunction.
What planetary science disciplines would this involve?
Planetary Geology, Planetary Atmospheres, Comparative Planetology
Point of contact for follow-on questions (Name and contact info)
Eliot Young (efy@boulder.swri.edu, 720-432-2333)