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Epsilon Eridani Planet Confirmed

Epsilon Eridani was a magic name in my childhood, so convinced was I that the nearby star (10.5 light years from Earth) was orbited by planets. Now the Hubble Space Telescope has weighed in with definitive evidence for the existence of at least one of those worlds, a Jupiter-class gas giant in a 6.9 year orbit around the star. The planet was originally detected in 2000 by radial velocity measurements, but there was still the faint possibility that turbulence on the star itself might mimic a planet’s effects.

Now we know that wasn’t so. G. Fritz Benedict and Barbara McArthur (University of Texas at Austin) led the team that announced the result. Those stellar wobbles tell an unmistakable story when observed over time. Here’s Benedict on the matter:

“You can’t see the wobble induced by the planet with the naked eye. But Hubble’s fine guidance sensors are so precise that they can measure the wobble. We basically watched three years of a nearly seven-year-long dance of the star and its invisible partner, the planet, around their orbits. The fine guidance sensors measured a tiny change in the star’s position, equivalent to the width of a quarter 750 miles away.”

No atmospheric effects there. Epsilon Eridani b is the real deal, an observation confirmed by combining the Hubble data with studies from a variety of telescopes made over the past 25 years. The work is precise enough that we not only have a confirmed detection but also a good read on the planet’s mass, which is found to be 1.5 times that of Jupiter. The planet moves at the same 30 degree tilt to our line of sight as the dust and debris disk surrounding Epsilon Eridani.

Epsilon Eridani planet

Image: NASA’s Hubble Space Telescope, in collaboration with ground-based observations, has provided definitive evidence for the existence of the nearest extrasolar planet to our solar system. The Jupiter-sized world orbits the Sun-like star Epsilon Eridani, which is only 10.5 light-years away. The results are being presented at the 38th Annual Division of Planetary Sciences Meeting in Pasadena, Calif. and will appear in the November issue of the Astronomical Journal. This is an artist’s concept of the Jupiter-mass planet orbiting the star. Credit: NASA, ESA, and G.F. Benedict (University of Texas, Austin).

Remember, this is a relatively young star, roughly 800 million years old, so its debris disk is still robust. Now we have a confirmed planet and a debris disk around the same star, compelling evidence that planets do indeed form out of such disks. The really exciting part? Hubble has a fighting chance to get an image of this planet in 2007, and so do other space-based cameras and even ground observatories. It will then be at periapsis — its closest approach to Epsilon Eridani — shining brightly in reflected starlight.

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  • ljk October 16, 2006, 10:53

    Astrophysics, abstract

    From: G. Fritz Benedict [view email]

    Date: Mon, 9 Oct 2006 15:09:44 GMT (511kb)

    The Extrasolar Planet epsilon Eridani b – Orbit and Mass

    Authors: G. Fritz Benedict, Barbara E. McArthur, George Gatewood, Edmund Nelan, William D. Cochran, Artie Hatzes, Michael Endl, Robert Wittenmyer, Sallie L. Baliunas, Gordon A. H. Walker, Stephenson Yang, Martin Kurster, Sebastian Els, Diane B. Paulson

    Hubble Space Telescope observations of the nearby (3.22 pc), K2 V star epsilon Eridani have been combined with ground-based astrometric and radial velocity data to determine the mass of its known companion. We model the astrometric and radial velocity measurements simultaneously to obtain the parallax, proper motion, perturbation period, perturbation inclination, and perturbation size. Because of the long period of the companion, \eps b, we extend our astrometric coverage to a total of 14.94 years (including the three year span of the \HST data) by including lower-precision ground-based astrometry from the Allegheny Multichannel Astrometric Photometer. Radial velocities now span 1980.8 — 2006.3. We obtain a perturbation period, P = 6.85 +/- 0.03 yr, semi-major axis, alpha =1.88 +/- 0.20 mas, and inclination i = 30.1 +/- 3.8 degrees. This inclination is consistent with a previously measured dust disk inclination, suggesting coplanarity. Assuming a primary mass M_* = 0.83 M_{\sun}, we obtain a companion mass M = 1.55 +/- 0.24 M_{Jup}. Given the relatively young age of epsilon Eri (~800 Myr), this accurate exoplanet mass and orbit can usefully inform future direct imaging attempts. We predict the next periastron at 2007.3 with a total separation, rho = 0.3 arcsec at position angle, p.a. = -27 degrees. Orbit orientation and geometry dictate that epsilon Eri b will appear brightest in reflected light very nearly at periastron. Radial velocities spanning over 25 years indicate an acceleration consistent with a Jupiter-mass object with a period in excess of 50 years, possibly responsible for one feature of the dust morphology, the inner cavity.


  • ljk March 14, 2007, 12:02

    Astrophysics, abstract

    From: Markus Janson [view email]

    Date: Tue, 13 Mar 2007 09:09:41 GMT (1460kb)

    NACO-SDI direct imaging search for the exoplanet Eps Eri b

    Authors: Markus Janson, Wolfgang Brandner, Thomas Henning, Rainer Lenzen, Barbara McArthur, G. Fritz Benedict, Sabine Reffert, Eric Nielsen, Laird Close, Beth Biller, Stephan Kellner, Eike Guenther, Artie Hatzes, Elena Masciadri, Kerstin Geissler, Markus Hartung

    Comments: 40 pages, 20 figures, accepted for publication in AJ

    The active K2V star $\epsilon$ Eri hosts the most nearby known extrasolar planet. With an angular separation of about 1″ on average, and an age of a few to several hundred Myrs, $\epsilon$ Eri b is one of the prime candidates for becoming the first definitive extrasolar planet imaged directly. We present a multi-epoch deep differential imaging survey performed with NACO-SDI at the VLT with the aim of finding the planet. The results are combined with recent astrometry in an attempt to further constrain the detection limits. No convincing candidate is found among the many coherent structures that constitute the residual speckle noise, which is the dominant noise at small angular scales. We present our detection limits, compare them with the estimated brightness of $\epsilon$ Eri b, and analyze how the limits can be improved further. It is found that integration time remains a very important parameter for achieving good results, even in the speckle-dominated regimes. The results yield new, improved upper 3$\sigma$ limits on the absolute H-band (1.6 $\mu$m) brightness of the 1.55 $M_{\rm jup}$ companion of 19.1 to 19.5 mag, depending on the specific age of the system.


  • ljk November 7, 2007, 13:02

    The differential rotation of epsilon Eri from MOST data

    Authors: H.-E. Froehlich

    (Submitted on 6 Nov 2007)

    Abstract: From high-precision MOST photometry spanning 35 days the existence of two spots rotating with slightly differing periods is confirmed.
    From the marginal probability distribution of the derived differential rotation parameter k its expectation value as well as confidence limits are computed directly from the data. The result depends on the assumed range in inclination i, not on the shape of the prior distributions.

    Two cases have been considered: (a) The priors for angles, inclination i of the star and spot latitudes beta_1,2, are assumed to be constant over i, beta_1, and beta_2. (b) The priors are assumed to be constant over cosi, sin beta_1, and sin beta_2. In both cases the full range of inclination is considered: 0^o less than = i less than = 90^o. Scale-free parameters, i.e. periods and spot areas (in case of small spots) are taken logarithmically. Irrespective of the shape of the prior, k is restricted to 0.03 less than = k less than = 0.10 (one-sigma limits). The inclination i of the star is photometrically ill-defined.

    Comments: 3 pages, 4 figures, Astron. Nachr. Vol. 328 (2007), acc

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0711.0806v1 [astro-ph]

    Submission history

    From: Guenther Ruediger [view email]

    [v1] Tue, 6 Nov 2007 07:34:07 GMT (38kb)


  • ljk November 27, 2007, 0:32

    The corona and upper transition region of epsilon Eridani

    Authors: J.-U. Ness, C. Jordan

    (Submitted on 24 Nov 2007)

    Abstract: We present analyses of observations of epsilon Eridani (K2 V) made with the Low Energy Transmission Grating Spectrometer on Chandra and the Extreme Ultraviolet Explorer, supplemented by observations made with the Space Telescope Imaging Spectrograph, the Far Ultraviolet Spectroscopic Explorer and the Reflection Grating Spectrometer on XMM-Newton. The observed emission lines are used to find relative element abundances, to place limits on the electron densities and pressures and to determine the mean apparent emission measure distribution. As in the previous paper by Sim & Jordan (2003a), the mean emitting area as a function of the electron temperature is derived by comparisons with a theoretical emission measure distribution found from energy balance arguments. The final model has a coronal temperature of 3.4 x 10^6 K, an electron pressure of 1.3 x 10^16 cm^-3 K at T_e = 2 x 10^5 K and an area filling factor of 0.14 at 3.2 x 10^5 K. We discuss a number of issues concerning the atomic data currently available. Our analyses are based mainly on the latest version of CHIANTI (v5.2).

    We conclude that the Ne/O relative abundance is 0.30, larger than that recommended from solar studies, and that there is no convincing evidence for enhanced coronal abundances of elements with low first ionization potentials.

    Comments: accepted by MNRAS; 19 pages, five figures, 10 tables

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0711.3805v1 [astro-ph]

    Submission history

    From: Jan-Uwe Ness [view email]

    [v1] Sat, 24 Nov 2007 01:38:20 GMT (86kb)


  • elliot April 25, 2008, 12:27

    this system is metioned in the halo book series

  • ljk June 13, 2008, 15:18

    Modeling $\epsilon$ Eridani and asteroseismic tests of element diffusion

    Authors: Ning Gai, Shao-Lan Bi, Yan-Ke Tang

    (Submitted on 11 Jun 2008)

    Abstract: Taking into account the helium and metal diffusion, we explore the possible evolutionary status and perform seismic analysis of MOST target: the star $\epsilon$ Eridani. We adopt the different input parameters to construct the models by fitting the available observational constraints: e.g., $T_{eff}$, $L$, $R$, $[Fe/H]$. From computation, we obtain the average large spacings of $\epsilon$ Eridani about $194\pm 1 \mu$Hz. The age of the diffused models has been found to be about 1 Gyr, which is younger than one determined previously by models without diffusion.

    We found that the effect of pure helium diffusion on the internal structure of the young low-mass star is slight, but the metal diffusion influence is obvious. The metal diffusion leads the models to have much higher temperature in the radiation interior, correspondingly the higher sound speed in the interior of the model, thereby the larger frequency and spacings.

    Comments: 16 pages, 4 figures, accepted for publication in ChjAA

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0806.1811v1 [astro-ph]

    Submission history

    From: Yanke Tang [view email]

    [v1] Wed, 11 Jun 2008 08:34:13 GMT (169kb)


  • ljk July 3, 2008, 16:40

    A comprehensive examination of the Eps Eri system — Verification of a 4 micron narrow-band high-contrast imaging approach for planet searches

    Authors: Markus Janson, Sabine Reffert, Wolfgang Brandner, Thomas Henning, Rainer Lenzen, Stefan Hippler

    (Submitted on 2 Jul 2008)

    Abstract: Due to its proximity, youth, and solar-like characteristics with a spectral type of K2V, Eps Eri is one of the most extensively studied systems in an extrasolar planet context. Based on radial velocity, astrometry, and studies of the structure of its circumstellar debris disk, at least two planetary companion candidates to Eps Eri have been inferred in the literature (Eps Eri b, Eps Eri c). Some of these methods also hint at additional companions residing in the system.

    Here we present a new adaptive optics assisted high-contrast imaging approach that takes advantage of the favourable planet spectral energy distribution at 4 microns, using narrow-band angular differential imaging to provide an improved contrast at small and intermediate separations from the star.

    We use this method to search for planets at orbits intermediate between Eps Eri b (3.4 AU) and Eps Eri c (40 AU). The method is described in detail, and important issues related to the detectability of planets such as the age of Eps Eri and constraints from indirect measurements are discussed. The non-detection of companion candidates provides stringent upper limits for the masses of additional planets. Using a combination of the existing dynamic and imaging data, we exclude the presence of any planetary companion more massive than 3 Mjup anywhere in the Eps Eri system.

    Specifically, with regards to the possible residual linear radial velocity trend, we find that it is unlikely to correspond to a real physical companion if the system is as young as 200 Myr, whereas if it is as old as 800 Myr, there is an allowed semi-major axis range between about 8.5 and 25 AU.

    Comments: 11 pages, 8 figures, A&A accepted

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0807.0301v1 [astro-ph]

    Submission history

    From: Markus Janson [view email]

    [v1] Wed, 2 Jul 2008 09:09:11 GMT (348kb,D)


  • ljk July 28, 2008, 1:18

    Deep L’ and M-band Imaging for Planets Around Vega and epsilon Eridani

    Authors: A. N. Heinze, Philip M. Hinz, Matthew Kenworthy, Douglas Miller, Suresh Sivanandam

    (Submitted on 24 Jul 2008)

    Abstract: We have obtained deep Adaptive Optics (AO) images of Vega and epsilon Eri to search for planetary-mass companions. We observed at the MMT in the L’ (3.8 micron) and M (4.8 micron) bands using Clio, a recently commissioned imager optimized for these wavelengths. Observing at these long wavelengths represents a departure from the H band (1.65 microns) more commonly used for AO imaging searches for extrasolar planets.

    The long wavelengths offer better predicted planet/star flux ratios and cleaner (higher Strehl) AO images, at the cost of lower diffraction limited resolution and higher sky background.

    We have not detected any planets or planet candidates around Vega or epsilon Eri. We report the sensitivities obtained around both stars, which correspond to upper limits on any planetary companions which may exist.

    The sensitivities of our L’ and M band observations are comparable to those of the best H-regime observations of these stars. For epsilon Eri our M band observations deliver considerably better sensitivity to close-in planets than any previously published results, and we show that the M band is by far the best wavelength choice for attempts at ground-based AO imaging of the known planet epsilon Eri b.

    The Clio camera itself with MMTAO may be capable of detecting epsilon Eri b at its 2010 apastron, given a multi-night observing campaign. Clio appears to be the only currently existing AO imager that has a realistic possibility of detecting epsilon Eri b.

    Comments: 45 pages, 15 figures, accepted to ApJ

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0807.3975v1 [astro-ph]

    Submission history

    From: Aren Heinze [view email]

    [v1] Thu, 24 Jul 2008 21:20:26 GMT (596kb)


  • ljk October 27, 2008, 23:35

    October 27, 2008

    Spock’s Solar System Looks Like Ours

    Written by Nancy Atkinson

    This artist’s conception shows the closest known planetary system to our own, called Epsilon Eridani. Credit: NASA/JPL/Caltech

    Back in 2000, astronomers discovered a Jupiter-sized planet orbiting the nearby star Epsilon Eridani. Since that star system is listed in some Star Trek lore as the location of the fabled planet Vulcan, astronomers joked they had found Spock’s homeworld.

    But enticing new discoveries of the Epsilon Eridani system implies it could be a younger twin to our own solar system. It has two rocky asteroid belts and an outer icy ring, making it a triple-ring system. The inner asteroid belt looks strikingly similar to the one in our solar system, while the outer asteroid belt holds 20 times more material.

    All of this material implies that unseen planets lie hidden, shaping the rings. But if another civilization possibly could have developed in this region, let’s hope they are more like Spock than Kirk’s evil twin….


    Apparently Universe Today made a boo-boo – Spock’s home world
    circles 40 Eridani, not Epsilon Eridani.

  • ljk October 27, 2008, 23:40

    Epsilon Eridani’s Planetary Debris Disk: Structure and Dynamics based on Spitzer and CSO Observations

    Authors: D. Backman, M. Marengo, K. Stapelfeldt, K. Su, D. Wilner, C. D. Dowell, D. Watson, J. Stansberry, G. Rieke, T. Megeath, G. Fazio, M. Werner

    (Submitted on 24 Oct 2008)

    Abstract: Spitzer and Caltech Submillimeter Observatory (CSO) images and spectrophotometry of epsilon Eridani at wavelengths from 3.5 to 350 um reveal new details of its bright debris disk. The 350 um map confirms the presence of a ring at r = 11-28 arcsec (35-90 AU) observed previously at longer sub-mm wavelengths.

    The Spitzer mid- and far-IR images do not show the ring, but rather a featureless disk extending from within a few arcsec of the star across the ring to r ~ 34 arcsec (110 AU). The spectral energy distribution (SED) of the debris system implies a complex structure. A model constrained by the surface brightness profiles and the SED indicates that the sub-mm ring emission is primarily from large (a ~ 135 um) grains, with smaller (a ~ 15 um) grains also present in and beyond the ring.

    The Spitzer IRS and MIPS SED-mode spectrophotometry data clearly show the presence of spatially compact excess emission at lambda > 15 um that requires the presence of two additional narrow belts of dust within the sub-mm ring’s central void. The innermost belt at r ~ 3 AU is composed of silicate dust. A simple dynamical model suggests that dust produced collisionally by a population of about 11 M_Earth of planetesimals in the sub-mm ring could be the source of the emission from both in and beyond the sub-mm ring. Maintaining the inner belts and the inner edge to the sub-mm ring may require the presence of three planets in this system including the candidate radial velocity object.

    Comments: To appear on The Astrophysical Journal

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0810.4564v1 [astro-ph]

    Submission history

    From: Massimo Marengo [view email]

    [v1] Fri, 24 Oct 2008 22:43:15 GMT (235kb)