Michigan-led search rules out Jupiter-mass planets in the inner regions of 70 Ophiuchi AB

The exclusion is lopsided. Around 70 Oph A it reaches 5 astronomical units, one astronomical unit being the Earth-sun distance, and around 70 Oph B it reaches half of one ^[3]. The cleared radius around A is therefore ten times the radius around B ^[1]. The limit covers bodies of Jupiter's mass or more. The phys.org account of the work says it holds with some important caveats, without listing them or placing either star's habitable zone relative to those radii ^[2].

The question stayed open because of the stars' radial velocity, their speed toward or away from Earth. Until this study, that measurement showed a wobble that a Jupiter-sized planet could explain, said Yiting Li, a postdoctoral researcher in the University of Michigan's astronomy department ^[15]. In the 171 years after William Jacob's 1855 claim, more sophisticated measurements had not ruled such a planet out of the inner regions ^[6][15].

The team had members at more than a dozen institutions, including NASA's Jet Propulsion Laboratory and IPAC at Caltech ^[14]. According to the university, it reached record sensitivity for this system ^[1]. "Yiting assembled an absolutely huge amount of data from all over the world and carefully explored all possibilities," said Michael Meyer, a senior co-author and chair of the department ^[18]. "It's a cautionary tale about how stellar activity can mimic planet signals using the radial velocity," he said ^[19].

The thing this doesn't tell you is whether a rocky planet is there. The search was not designed to find smaller planets ^[4]. Worlds the size of Saturn or smaller could still sit in the habitable zone, the region where temperatures would allow liquid water on a rocky planet's surface ^[5]. "It's a mix of disappointment and excitement," Li said ^[7]. "We're finding out that there isn't a Jupiter-sized planet, but we're also opening the latest chapter on this historic system." ^[8]

Proximity is the system's appeal, according to the university. At about 16 light-years it is the third-closest binary to Earth, after Alpha Centauri at 4.2 light-years and 61 Cygni at 11.4 ^[10]. Roughly half of the stellar systems in the Milky Way have at least two stars ^[9]. "The new limit enables us to design optimum search strategies in the future," Meyer said ^[12]. He went on: "In fact, the University of Michigan is part of a team studying a space mission called SHERA that will focus on binaries, where this system is one of a handful of targets. 70 Oph AB will certainly be a target of flagship missions, such as NASA's Habitable World Observatory." ^[13]

In my view the result sharpens the plan for this one system and leaves it on the target list ^[13]. A team pointing a future observatory at 70 Oph A can drop a Jupiter inside 5 AU from its model of the system ^[3]. It also has reason to treat radial-velocity wobbles from either star with caution. Surface variations on these same stars produced the wobble that had passed for a possible giant ^[17].