Janus Satellite Mission to Explore the Earth-Sun System from L1 Orbit

Last updated April 10, 2005

Janus is a mission proposed to NASA that will provide the first comprehensive and continuous observation of the Earth's whole dayside atmosphere, the solar wind, and the Sun from the Lagrange-1 orbit. That orbit, 1.5 million km away from the Earth along the Earth-Sun line, allows for continuous observation of the Earth's sunlit disk. The satellite rotates around the Sun with the same period as the Earth, so you always remain in the Earth-Sun line and can watch the Earth rotate, the sunlit disk continuously in your view. Occasionally the Moon (400,000 km away from the Earth) comes into the field of view and you get the picture at top left.

Janus will enable the first detailed exploration of the couplings within the Earth-Sun system. Continuous observation of tropospheric composition from L1 will yield a unique vantage point for mapping emissions of environmentally important species (including CO2, CH4, CO, NOx, VOCs, aerosols), and for tracking natural and pollution plumes over scales extending to the dimension of the Earth. Concurrent observations of the middle and upper atmosphere will afford a whole-atmosphere perspective on climate dynamics, ionization, photochemistry, and the global electric circuit. At the same time, the mission will provide continuous observations of solar activity (flares, CMEs, XUV irradiance), of the associated space weather (sampled in situ), and of the resulting impacts on the Earth's upper atmosphere. The Earth-viewing portion of the mission will consist of a combination of spectrometers in an extended wavelength range (58 nm to 2.4 mm). It will use a high-precision (1 nm surface smoothness) 0.5-meter parabolic primary mirror to obtain 5 km spatial resolution on the entire sunlit Earth disk. The space weather instrument suite will consist of a magnetometer capable of high time resolution measurement of magnetic field fluctuations and shocks, and two Faraday cup particle energy analyzers capable of measuring energy resolved charged particle spectra. Solar observations will be accomplished using an EUV spectrometer, a white light solar coronagraph, and a soft x-ray irradiance spectrometer.

Investigators:

• Daniel J. Jacob (Harvard University)
• Jay Herman, O.C. St. Cyr, Joseph Davila (NASA/GSFC)
• Clarence Korendyke, James Bishop, David Sisking (Naval Research Lab)

Janus Mission White Paper prepated for the NRC Decadal Survey (pdf)

NEVER LOSE AN OPPORTUNITY TO INCREASE YOUR CULTURE! Janus is the Roman god of doors and is represented as a head with two faces (picture at top right). With one face looking at the Earth and the other at the Sun, he is the perfect symbol for our mission!