Spacecraft instruments play a vital role in the field of astronomy, allowing scientists to gather valuable data about the universe. However, designing, building, and testing these instruments is a time-consuming process that often takes years. In a remarkable turn of events, a last-minute modification to one of the instruments on the European Space Agency’s (ESA) Solar Orbiter has opened up new possibilities for observing the Sun. This unexpected breakthrough was made possible by the ingenuity of an astronomer and a simple hack involving an instrument door.
Launched in February 2020, the Solar Orbiter aims to study the Sun’s inner heliosphere and polar regions with unprecedented resolution. The spacecraft undergoes a close approach to the Sun every six months, repeatedly studying the same region. This allows scientists to monitor the build-up of magnetic activity, which serves as a precursor to solar flares and eruptions. Among the suite of instruments carried by the Solar Orbiter is the Extreme Ultraviolet Imager (EUI), contributed by Belgium, which captures images of the Sun’s atmosphere from the chromosphere to the corona.
Traditionally, one of the biggest challenges in observing the Sun is the overwhelming brightness of the star itself. To overcome this obstacle, telescopes often utilize coronagraphs to block out the intense light and reveal finer details of the Sun’s atmosphere. During the final construction phase of the EUI, a team member had an ingenious idea: modifying the instrument’s safety door to enhance its functionality. By adding a small protrusion, or “thumb,” to the door, the EUI could partially cover the Sun’s bright disc when the door was halfway opened. This modification, deemed a “hack,” has proven immensely successful.
The addition of the thumb and the half-opened door created a new mode of operation for the EUI, aptly named the “occulter mode.” In this mode, the thumb obstructs the overpowering light from the Sun’s disc, allowing the EUI to detect the much fainter ultraviolet (UV) light coming from the surrounding corona. This breakthrough enables the instrument to capture deeper images of the Sun’s atmosphere, providing valuable insights into the physics and magnetic structures within this previously unexplored region.
The EUI, with its modified door, effectively combines the functionalities of a coronagraph and a camera into a single instrument. Previously, these two components were separate, but the EUI’s innovative design paves the way for a new generation of instruments capable of simultaneously imaging the Sun and its corona. The results of the team’s tests in this mode have been published in the journal Astronomy and Astrophysics, with Frédéric Auchère, the astronomer behind the hack, leading the research.
The modified EUI’s ability to capture images of the Sun’s atmosphere in the extreme ultraviolet (EUV) range unlocks a treasure trove of new knowledge. The depths of the Sun’s atmosphere, previously beyond the view of most extreme UV imagers, can now be explored with greater ease. This region is known to undergo dynamic changes in magnetic structures, making it an area of great scientific interest. With the improved imaging capabilities of the EUI’s occluder mode, scientists anticipate uncovering the secrets hidden within the Sun’s atmosphere.
Despite its breakthrough capabilities, the modified EUI does have some limitations. The late addition of the thumb to the instrument’s door means that it is currently in a sub-optimal position, leading to longer exposure times. Some test images in the published paper required exposures of up to 1000 seconds. However, with further refinements, future instruments and missions can overcome these limitations and improve efficiency. The authors of the paper suggest that with minor modifications, the exposure time could be reduced to 10 seconds, vastly increasing the efficiency of future EUV instruments.
The success of the modified EUI offers numerous advantages over traditional visible light (VL) instruments and coronagraphs. The absence of background emission from dust scattering significantly improves instrument performance and reduces the demands on platform pointing accuracy and stability. With these advantages in mind, EUV instruments have the potential to replace VL instruments and coronagraphs in solar imaging. This shift in solar observation techniques is poised to revolutionize our understanding of the Sun and unlock new discoveries.
The last-minute hack involving the modification of the Solar Orbiter’s EUI instrument door has opened up exciting possibilities for solar imaging. The unforeseen breakthrough, driven by the ingenuity of an astronomer, has led to the creation of a new mode of operation and instrument design. By partially blocking the intense light from the Sun’s disc, the modified EUI can capture unparalleled images of the Sun’s atmosphere, shedding light on previously unexplored regions. While there are limitations to the current design, the success of the modified EUI paves the way for future improvements and the development of more efficient EUV instruments. As we embark on this new era of solar observation, our understanding of the Sun’s dynamics and the mysteries hidden within its atmosphere is set to expand exponentially.
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