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Smile begins science operations before its X-ray camera can image the magnetopause
ESA cleared the joint European-Chinese Smile mission for science on 23 September, after 95 days of commissioning in orbit. Its aurora camera is recording now, while the X-ray imager meant to map the magnetopause waits for stray light to fade in mid-October.
The Scientist · Science desk
What happened
- During commissioning, European and Chinese teams deployed mechanisms, switched on units, checked ground communications and fixed the problems that came up.
- Pointed at Earth, SXI detects too much stray light, so ESA, the instrument consortium and the Chinese operations team are changing its settings and software onboard.
- Stray light is also falling on its own as Smile points farther from Earth and the North Pole gives off less light heading into winter.
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Why it matters
- constraint For the first weeks of science, Smile's record of the solar wind's effect on Earth comes from the aurora side; the X-ray view of the boundary itself has to wait.
- exposure Part of the stray-light drop depends on the dark northern winter, so whether SXI works year-round depends on the onboard software changes.
- capability A 45-hour continuous ultraviolet view of the full auroral ring, unavailable since 2008, lets researchers follow a geomagnetic disturbance for nearly two days at a stretch.
The instrument meant to picture the solar wind hitting Earth is the soft X-ray imager, SXI, a key European contribution to Smile [9]. Its targets are the magnetopause, where the solar wind meets Earth's magnetic field, and the northern polar cusp [12]. The cusp is a hole in the magnetosphere over the North Pole, where solar wind particles are funnelled toward the surface [12]. Smile's other three instruments are an ultraviolet aurora imager, a magnetometer and a light ion analyser [6].
So far SXI has been checked against the remains of an exploded star, far from Earth [9]. ESA says those images show the camera itself is working very well [9]. That is a different test from an image with Earth in the field of view, and Earth-pointed images are where the stray light appears [10]. ESA expects the stray light to reach its minimum in mid-October. At that point, the agency says, SXI would take its first good image of the magnetopause or the cusp [11]. That is about three weeks after the mission was cleared for science [2].
ESA did not say how much of the October improvement it credits to the onboard changes and how much to geometry and season. The split matters for the rest of the mission. Less light from the North Pole comes with the approaching northern winter [11], so I'd expect that part of the gain to reverse once the pole is back in sunlight. After that, SXI's Earth-pointed images depend on the new settings and software, and on a design ESA says can be adjusted remotely [10].
The aurora camera has had no comparable wait. Its 2008 benchmark means an 18-year gap in full-ring ultraviolet coverage of the northern lights [7][3]. The first footage ESA released was taken on 24 July, two weeks after UVI was switched on. It shows the auroral ring stirred up when a rush of solar wind particles disturbed Earth's magnetic field [8]. ESA calls the camera's 45-hour recording span record-breaking [7].
Smile, the Solar wind Magnetosphere Ionosphere Link Explorer, is a joint mission of ESA and the Chinese Academy of Sciences [13]. It launched on 19 May and reached its target orbit on 20 June [2], so in-orbit commissioning took 95 days before the 23 September clearance [1][1]. "Smile is now approved to begin science operations," said Carole Mundell, ESA's Director of Science [4]. "I am sure our excellent collaboration will deliver ground-breaking data to scientists around the world," she said [5].
What to watch
- Whether SXI returns a usable magnetopause or cusp image around the mid-October stray-light minimum.
- How SXI's Earth-pointed stray light behaves after the onboard software changes, once the North Pole moves back toward summer.
- When ESA and the Chinese Academy of Sciences start releasing Smile science data to outside researchers.