Images of a fourth planet orbiting HR 8799

By C. Marois, B. Zuckerman, Q. Konopacky, B. Macintosh, Travis S. Barman. Nature, 2010

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High-contrast near-infrared imaging of the nearby star HR 8799 has shown three giant planets. Such images were possible because of the wide orbits (>25 astronomical units, where 1 au is the Earth–Sun distance) and youth (<100 Myr) of the imaged planets, which are still hot and bright as they radiate away gravitational energy acquired during their formation. An important area of contention in the exoplanet community is whether outer planets (>10 au) more massive than Jupiter form by way of one-step gravitational instabilities or, rather, through a two-step process involving accretion of a core followed by accumulation of a massive outer envelope composed primarily of hydrogen and helium. Here we report the presence of a fourth planet, interior to and of about the same mass as the other three. The system, with this additional planet, represents a challenge for current planet formation models as none of them can explain the in situ formation of all four planets. With its four young giant planets and known cold/warm debris belts, the HR 8799 planetary system is a unique laboratory in which to study the formation and evolution of giant planets at wide (>10 au) separations.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/2d736ac368f6da65f5d30132ce9c2905543932b9

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RESOLVED IMAGES OF LARGE CAVITIES IN PROTOPLANETARY TRANSITION DISKS (2011, background): “Moreover, those companions would provide youthful touchstones that could help facilitate a better understanding of their much older counterparts, including the Fomalhaut and HR 8799 planets that orbit just inside their own remnant debris disk rings (Kalas et al. 2008; Marois et al. 2008, 2010).”
Imaging Extrasolar Giant Planets (2016, methodology): “…pipelines with additional features aimed at minimizing biases and avoiding both self- and over-subtraction of planet flux in ADI and SDI datasets (Marois et al. 2010a; Amara & Quanz 2012; Pueyo et al. 2012; Meshkat et al. 2013a; Wahhaj et al. 2013a; Brandt et al. 2013; Fergus et al. 2014; Mawet…”
Rapid inward migration of planets formed by gravitational instability (2011, background): “Since the latter requires a high brightness contrast between the planet and the parent star, massive planets have been observed at separations & 10 AU (e.g., Kalas et al. 2008; Marois et al. 2008; Lagrange et al. 2010; Lafrenière et al. 2010; Marois et al. 2010).”
Rapid growth of gas-giant cores by pebble accretion (2012, background): “In fact, we see that gas giants form both rapidly (Kraus & Ireland 2012) and at large orbital radii (Marois et al. 2010).”
THE GEMINI/NICI PLANET-FINDING CAMPAIGN: THE FREQUENCY OF PLANETS AROUND YOUNG MOVING GROUP STARS (2013, background): “However, all known directly imaged planets at these ages (specifically 2MASS 1207b and the HR 8799 planets; Chauvin et al. 2005a; Marois et al. 2008, 2010) have lacked methane absorption and show extremely red colors, likely due to dust clouds and/or non-equilibrium chemistry in their atmospheres…”
TRANSIT TIMING OBSERVATIONS FROM KEPLER. IV. CONFIRMATION OF FOUR MULTIPLE-PLANET SYSTEMS BY SIMPLE PHYSICAL MODELS (2012, background): “…of architecture has been building on several different fronts: radial velocity detections (HD 40307: Mayor et al. 2009; GJ 876: Rivera et al. 2010; HD 20794: Pepe et al. 2011), and a dramatic 4-planet system discovered by direct imaging (HR 8799: Fabrycky & Murray-Clay 2010b; Marois et al. 2010).”
PLANETS AROUND LOW-MASS STARS (PALMS). IV. THE OUTER ARCHITECTURE OF M DWARF PLANETARY SYSTEMS (2014, methodology): “Following the discoveries of planets orbiting the A-type stars HR 8799, Fomalhaut, and β Pic (Marois et al. 2008; Kalas et al. 2008; Marois et al. 2010b; Lagrange et al. 2010), high-mass stars have received the most attention in direct imaging planet searches (Ehrenreich et al. 2010; Janson et al.…”
TRANSITIONAL DISKS AS SIGNPOSTS OF YOUNG, MULTIPLANET SYSTEMS (2011, background): “Indeed, gaps in debris disks surrounding main-sequence stars harbor the giant planets Fomalhaut b (Kalas et al. 2008), ǫ Eridani b (Hatzes et al. 2000), the HR 8799 system (Marois et al. 2008, 2010) and β Pictoris b (Lagrange et al. 2010).”
SIMULTANEOUS DETECTION OF WATER, METHANE, AND CARBON MONOXIDE IN THE ATMOSPHERE OF EXOPLANET HR 8799 b (2015, background): “The HR8799 planetary system remains unique as the only system to have multiple, directly imaged, planets (Marois et al. 2008, 2010).”
Separating gas-giant and ice-giant planets by halting pebble accretion (2014, background): “In such a case, wide-orbit gas giants, such as the four planets around the A star HR8799 located at a = 15−70 AU (Marois et al. 2010), can form in situ.”
TESTING IN SITU ASSEMBLY WITH THE KEPLER PLANET CANDIDATE SAMPLE (2013, background): “…more characteristic of the planets in our own solar system (Butler & Marcy 1996; Boisse et al. 2012), at great distances from their host stars (Udalski et al. 2005; Gaudi et al. 2008; Kalas et al. 2008; Marois et al. 2008, 2010), and potentially even as free-floating objects (Sumi et al. 2011).”
First light of the VLT planet finder SPHERE - III. New spectrophotometry and astrometry of the HR 8799 exoplanetary system (2015, methodology): “The relative photometry of HD 1160 BC was derived using the method of the “negative synthetic companions” (Marois et al. 2010a; Bonnefoy et al. 2011).”
MODEL ATMOSPHERES FOR MASSIVE GAS GIANTS WITH THICK CLOUDS: APPLICATION TO THE HR 8799 PLANETS AND PREDICTIONS FOR FUTURE DETECTIONS (2011, background): “We do not consider the recently discovered fourth companion HR 8799e (Marois et al. 2010), for which data are presently inadequate for a detailed atmospheric analysis.”
The great escape: how exoplanets and smaller bodies desert dying stars (2011, background): “The discoveries of the four planets with a ≈ 15, 24, 38, 68 au orbiting HR 8799 (Marois et al. 2008, 2010) and the a ≈ 115 au planet orbiting Formalhaut (Kalas et al. 2008) revealed that wide-orbit (a > 10–100 au) planets do exist and incited great interest in their formation and evolution.”
The Gemini Planet Imager Exoplanet Survey: Giant Planet and Brown Dwarf Demographics from 10 to 100 au (2019, background): “…and data reduction (Lafrenière et al. 2007; Soummer et al. 2012; Wang et al. 2015; Pueyo 2016) have led to detections of planets orbiting HR 8799 (Marois et al. 2008, 2010), β Pictoris (Lagrange et al. 2009), HD 95086 (Rameau et al. 2013a, 2013b), 51 Eridani (Macintosh et al. 2015), and HIP…”
THE TUCANA/HOROLOGIUM, COLUMBA, AB DORADUS, AND ARGUS ASSOCIATIONS: NEW MEMBERS AND DUSTY DEBRIS DISKS (2011, background): “HIP 114189 (= HR 8799) is known to be orbited by a multiple system of massive planets imaged by Marois et al. (2008, 2010) and by a massive dusty debris disk (Rhee et al 2007a, Su et al 2009).”
LkCa 15: A YOUNG EXOPLANET CAUGHT AT FORMATION? (2011, result): “The same result has been found for moderately older direct-imaged exoplanets, such as Beta Pic b (Lagrange et al. 2009; Quanz et al. 2010; Currie et al. 2011a) and HR 8799 bcde (Marois et al. 2008; Bowler et al. 2010; Marois et al. 2010; Currie et al. 2011b; Madhusudhan et al. 2011).”
DISCOVERY OF A PROBABLE 4–5 JUPITER-MASS EXOPLANET TO HD 95086 BY DIRECT IMAGING (2013, background): “HD95086b, HR8799 cde, and 2M1207b appears to be similar in the sense that they all lie at the L -”