Welcome to the Solar System twilight observing program at Keck Observatory!

The Targets

Here are some examples of recent data:

Io Titan Uranus Neptune
View all Io images View all Titan images View all Uranus images View all Neptune images

The Program

Our solar system is a diverse and dynamic place. From the volcanic eruptions on Io to the massive storm systems of Uranus and Neptune and Titan‘s seasonal clouds, many planetary phenomena take place rapidly and change from week to week or even day to day. Understanding these phenomena, including the physics that governs them and how they change over time, requires frequent and closely-spaced (cadenced) observations. Solar system objects are much brighter than many astrophysical targets, and the Keck telescopes 10-meter mirrors allow high-quality images to be obtained in only a few minutes‘ time. The infrared wavelengths detected by the NIRC2 and OSIRIS instruments are perfectly suited to observations of this type: Io‘s hot volcanoes shine brightly in the infrared, and the specific properties of molecules like methane and ammonia mean that infrared images of dense atmospheres contain information on their compositions. We also take advantage of Keck‘s adaptive optics system, which turns a blurry disk of light into the crisp, high-resolution images shown above. Click on the view all images buttons above to learn more about our science objectives for each planet or moon.

Click on the links below to view recent press releases from our team:

Five-year record of volcanic activity on Io (2019)
New storm makes surprise appearance on Neptune (2017)
Long-term, hi-res tracking of eruptions on Io (2016)
Massive eruptions on Io (2014)
Extreme storms on Uranus (2014)


de Kleer, K.*, de Pater, I.*, Molter, E. M.*, Banks, E., Davies, A. G., Alvarez, C.*, Campbell, R.*, Aycock, J.^, Pelletier, J.^, Stickel, T.^, Kacprzak, G. G.+, Nielsen, N. M.+, Stern, D.+, Tollefson, J.+ (2019). Io's Volcanic Activity from Time Domain Adaptive Optics Observations: 2013-2018. The Astronomical Journal, 158(1), 29.

Molter, E.* de Pater, I.*, Luszcz-Cook, S., Hueso, R., Tollefson, J., Alvarez, C.*, Sanchez-Lavega, A., Wong, M. H., Hsu, A. I., Sromovsky, L. A., Fry, P. M., Delcroix, M., Campbell, R.*, de Kleer, K.*, Gates, E., Lynam, P. D., Ammons, S. M.+, Coy, B. P.+, Duchene, G.+, Gonzalez, E. J.+, Hirsch, L.+, Magnier, E. A.+, Ragland, S.+, Rich, M.+, Wang, F.+ (2019). Analysis of Neptune's 2017 bright equatorial storm. Icarus, 321, 324-345.

Chavez E., Redwing, E.*, de Pater, I.*, Hueso, R., Molter, E. M.*, Wong, M. H., Alvarez, C.*, Gates, E., de Kleer, K.*, Aycock, J.^, Mcilroy, J.^, Pelletier, J.^, Ridenour, A.^, Sanchez-Lavega, A., Rojas, J. F., Terry Stickel, T.^ (2023). Drift rates of major Neptunian features between 2018 and 2021. Icarus, 401, 115604.

Chavez, E., de Pater, I.*, Redwing, E.*, Molter, E. M.*, Roman, M. T., Zorzi, A., Alvarez, C.*, Campbell, R.*, de Kleer, K.*, Hueso, R., Wong, M. H., Gates, E., Lynam, P. D., Davies, A. G., Aycock, J.^, Mcilroy, J.^, Pelletier, J.^, Ridenour, A.^, Stickel, T.^ (2023). Evolution of Neptune at near-infrared wavelengths from 1994 through 2022. Icarus, 404, 115667.

Nixon, C. A., Bézard, B., Cornet, T., Park Coy, B., de Pater, I.*, Es-Sayeh, M., Hammel, H. B., Lellouch, E., Lombardo, N., López-Puertas, M., Lora, J. M., Rannou, P., Rodriguez, S., Teanby, N. A., Turtle, E. P., Achterberg, R. K., Alvarez, C.*, Davies, A. G., de Kleer, K.*, Doppmann, G.+, Fletcher, L. N., Hayes, A. G., Holler, B. J., Irwin, P. G. J., Jordan, C.^, King, O. R. T., Kutsop, N. W., Marlin, T., Melin, H., Molter, E. M.*, Moore, L.+, O'Donoghue, J.+, O'Meara, J+, Milam, S. N., Rafkin, S. C. R, Roman, M. T., Rostopchina, A.^, Rowe-Gurney, N., Schmidt, C., Schmidt, J., Sotin, C., Stallard, T. S.+, Stansberry, J. A., West, R. A. (2024). Titan's Atmosphere in Late Northern Summer from JWST and Keck Observations. Nature Astronomy, Submitted.

* member of the Twilight Zone Team
^ Keck Observing Assistant
+ Clasically scheduled observers who donated time

The Twilight Zone Team

For Observers

We would like to invite your participation in obtaining cadence data of time-variable planets and satellites! Press the Plan Observations button to generate observing information and instructions for a specific date.

Select instrument: NIRC2 OSIRIS This pulls data from another webpage and so may take up to a minute to resolve

Possible instrument combinations:

TZ observations during twilights are more suited for nights when the classically-scheduled program uses an optical instrument (LRIS, HIRES, DEIMOS or KCWI).

TZ observations in cloudy conditions any time during the night can potentially be perfomed when the classically-scheduled instrument is any of the above, if the classically-scheduled observing team donates the time.

Important note: The function to download the target list to the WMKO starlist directory will only work if you are in the internal Keck network and access the planning area using the Twilight Zone web site running on the Keck internal web server.