Interface Region Imaging Spectrograph

Lore & Background

IRIS was selected on 19 June 2009 from six Small Explorer mission candidates for further study, along with the Gravity and Extreme Magnetism (GEMS) space observatory. The spacecraft arrived at Vandenberg Air Force Base, California, on 16 April 2013 and was successfully deployed from an Orbital L-1011 carrier aircraft flying over the Pacific Ocean at an altitude of 12,000 m, roughly 160 km northwest of Vandenberg. The launch vehicle was dropped at 02:27:46 UTC on 28 June 2013 by a Pegasus-XL launch vehicle.

The spacecraft consists of a satellite bus and spectrometer built by the Lockheed Martin Solar and Astrophysics Laboratory, and a telescope provided by the Smithsonian Astrophysical Observatory. The IRIS instrument is a multi-channel imaging spectrograph with a 19 cm ultraviolet telescope, obtaining spectra along a slit and slit-jaw images. Its far-ultraviolet channel covers 133.2-135.8 nm and 139.0-140.6 nm, while the near-ultraviolet channel covers 278.5-283.5 nm. The baseline cadence is 5 seconds for slit-jaw images and 1 second for six spectral windows.

IRIS achieved first light on 17 July 2013. NASA noted that its first images showed a multitude of thin, fibril-like structures never seen before, revealing enormous contrasts in density and temperature. On 31 October 2013, calibrated IRIS data and images were released on the project website. Data collected has shown the interface region of the Sun is significantly more complex than previously thought, including features described as solar heat bombs, high-speed plasma jets, nano-flares, and mini-tornadoes. In 2019, IRIS detected tadpole-like jets coming out from the Sun.

Reader's Guide

IRIS is significant as a dedicated solar observatory that provides high-resolution ultraviolet spectra and images of the Sun's chromosphere and transition region, areas critical to understanding how energy and plasma flow into the corona and heliosphere. Its high-frame-rate ultraviolet imaging spectrometer, offering one image per second at 0.3-arcsecond angular resolution, has revealed previously unseen structures such as thin fibril-like features and enormous contrasts in density and temperature. The mission's science results, including the discovery of solar heat bombs, high-speed plasma jets, nano-flares, and mini-tornadoes, have advanced understanding of non-thermal energy transfer in the lower solar atmosphere. By addressing questions about the types of non-thermal energy dominating the chromosphere, how the chromosphere regulates mass and energy supply to the corona, and the role of magnetic flux emergence in flares and mass ejections, IRIS contributes directly to Sun-Earth connection studies. Its legacy includes a wealth of calibrated data released publicly and an open-access article in Solar Physics, with a large international team spanning multiple institutions and agencies.

Did You Know?

• IRIS was selected from six Small Explorer mission candidates for further study on 19 June 2009.
• The spacecraft was deployed from an Orbital L-1011 carrier aircraft at an altitude of 12,000 m over the Pacific Ocean.
• IRIS achieved first light on 17 July 2013, revealing thin, fibril-like structures never seen before.

Mission & Scientific Objectives

IRIS was conceived as a focused NASA Small Explorer mission to probe one of the Sun's most poorly understood layers. Rather than studying the entire solar disk, the spacecraft zeroes in on the interface region at the solar limb—the thin band encompassing the chromosphere and transition region. The overarching goal is to trace how energy and plasma flow upward from this layer into the corona and beyond into the heliosphere, a process for which suitable observations had previously been lacking. Three specific questions guide the science program: identifying which forms of non-thermal energy dominate in the chromosphere and above; understanding how the chromosphere acts as a gatekeeper, regulating the supply of mass and energy delivered to the corona and solar wind; and determining how magnetic flux and matter emerge through the lower solar atmosphere, including the role that flux emergence plays in triggering flares and coronal mass ejections. All of this is accomplished with a single, highly capable multi-channel imaging spectrograph, making IRIS a compact but scientifically ambitious addition to the Sun-Earth connection research portfolio.

Instrument & Technical Capabilities

The heart of IRIS is a multi-channel ultraviolet imaging spectrograph built around a 19-centimeter telescope supplied by the Smithsonian Astrophysical Observatory, with the spectrometer itself constructed by Lockheed Martin's Solar and Astrophysics Laboratory. The instrument captures spectra along a slit roughly one-third of an arcsecond wide while simultaneously recording slit-jaw images through four narrow passbands in both the far-ultraviolet and near-ultraviolet ranges. Its charge-coupled device detectors feature pixels of one-sixth arcsecond, yielding an effective spatial resolution between 0.33 and 0.40 arcsecond across a maximum field of view of 120 arcseconds. Spectral resolution reaches 0.04 nanometers in the far-UV channel (covering 133.2–135.8 nm and 139.0–140.6 nm) and 0.08 nanometers in the near-UV channel (278.5–283.5 nm). The system sustains a high average data rate of 0.7 megabits per second, enabling a baseline cadence of just one second for six spectral windows and five seconds for slit-jaw imaging, with rapid rastering available to map larger solar regions.

Launch & First Light

After arriving at Vandenberg Air Force Base in California on 16 April 2013, IRIS spent its final weeks in pre-flight preparations before a dramatic air-launch deployment. On the evening of 27 June 2013 (7:27 p.m. Pacific Daylight Time, recorded as 02:27:46 UTC on 28 June), a Pegasus-XL rocket was released from an Orbital L-1011 carrier aircraft cruising at 12,000 meters over the Pacific Ocean, roughly 160 kilometers northwest of Vandenberg. The successful deployment marked the beginning of IRIS's operational life. Just under three weeks later, on 17 July 2013, the spacecraft achieved first light. NASA highlighted that those initial images revealed a profusion of thin, fibril-like structures never previously observed, showing that density and temperature can vary dramatically even between adjacent loops just a few hundred miles apart. Calibrated data and images were made publicly available on the project website on 31 October 2013, and an open-access paper describing the satellite and its early observations appeared in the journal Solar Physics.

Discoveries & Scientific Impact

Since its 2013 launch, IRIS has fundamentally reshaped how researchers view the solar interface region. Observations have demonstrated that this layer is far more dynamic and structurally complex than earlier models suggested. Among the phenomena catalogued by the spacecraft are so-called solar heat bombs, high-speed plasma jets, nano-flares, and mini-tornadoes—each representing a distinct mechanism through which energy is transported toward the corona. These findings constitute a critical step in understanding how the Sun's outer atmosphere is heated. In 2019, IRIS captured striking tadpole-shaped jets erupting from the solar surface, further enriching the catalog of previously unseen structures. The mission's success is underpinned by a broad international collaboration spanning institutions such as the Smithsonian Astrophysical Observatory, Montana State University, the University of Oslo, Stanford University, Princeton Plasma Physics Laboratory, the European Space Agency, the Max Planck Institute for Solar System Research, and numerous other universities and research centers across the globe, all coordinated through Lockheed Martin's Solar and Astrophysics Laboratory and NASA's Ames Research Center.