About JASMINE

Main science objective of JASMINE is Galactic Center Archaeology, to understand the formation and evolution history of our habitat, th Milky Way galaxy. JASMINE measure the precise position and motion of stars in the Galactic nucleus region, which is the core of the Milky Way. Unveiling the spatial distribution and motions for stars in the Galactic center, where the formation of stars are retained since the beginning of the Milky Way, will enable us to uncover the formation and history of the Milky Way. Understanding the formation processes of the Milky Way will also help us to understand the formation of the other galaxies.

To achieve this science objective, JASMINE is designed as follows.

In Space (launched in the late 2020s):

JASMINE will be a space astrometry mission, and the nominal operation period is planned to be 3 years.

Near-infrared Astrometry (1.1-1.6 microns):

Galactic nucleolus region is hidden in the optical band due the heavy dust extinction. JASMINE will observe in near-infrared band, where the dust extinction is low. European Space Agency (ESA)'s Gaia mission is operating in the optical band, and Gaia cannot study the Galactic nucleus region. Therefore, JASMINE will provide complementary and crucial information about the center of our Galaxy.

Targeting the Nuclear Bulge (Galactic Centeral Region):

JASMINE will achieve the accuracies of 25 µarcsec in annual parallax (distance) and 25 µarcsec/yr in proper motion (tangential velocity) measurement for stars in the Galactic center.

• 25 µarcsec = 1/144,000,000 degree. This is equivalent to be able to resolve the 1/10 of the width of a hair of a person at the top of Mt. Fuji from Tokyo Skytree.
• This will be achieved by observing the same field a large number of times, and combining these images. There will be 320 times exposures for 16 fields in one day, and 460 thousands exposures in one season (~90 days).

Public Star Catalog (released in the early 2030s):

The final catalog of the position and motions of all the stars observed by JASMINE will be publicly released, which will be valuable for wide areas of sciences in astronomy.

Science

Galactic Center Archaeology (Astrometry)

Structure of the Galactic nuclear bulge and formation epoch of the Galactic bar.

The world-first near-infrared Galactic center astrometry mission, JASMINE will reveal the detailed structure of the Galactic center region, so-called Galactic nuclear bulge, whose structure and the formation history are still mystery and veiled with the heavy dust extinction. One of the interesting structures in the Galactic center region is a Galactic nuclear disk, which is considered to be formed when the Galactic bar formed. JASMINE will uncover the age distribution of the Mira variable stars in the Galacitc nuclear disk, and identify the formation epoch of the nuclear disk, and therefore the formation epoch of the Galactic bar. (see Baba & Kawata, 2020, MNRAS, 492, 4500)

Gas inflow to a super-massive black hole

There is a super-massive black hole (SMBH) with about 4 million times more massive than the Sun at the center of our Galaxy. However, how the SMBH is growing is not known. JASMINE will reconstruct the mass distribution, non-axisymmetry and rotation properties of the Galactic nuclear bulge. From these properties we will study how and how much the gas is falling into the Galactic center and feeding the SMBH.

Relic of super-massive black hole formation

One of the potential formation scenarios of the SMBH is a successive mergers of massive black holes. If the SMBH of the Milky Way formed through this mechanism, such mergers must strongly impact on the kinematics of the stars in the Galactic center region. JASMINE will measure the precise position and motion of stars in the Galacic center region, which would be enough to tell such impact, and therefore JASMINE will tell us if or not our SMBH formed via mergers.

Hidden star clusters

The accurate proper motion, tangential motion in the sky, measurements of stars in the Galactic center enable us to find hidden star clusters not possible to be identified with photometric surveys. The proper motion data enable us to identify star clusters, even the ones dissolving, as groups of stars moving coherently. The orbit and age of the star clusters will help us to uncover the formation and evolution history of the Galactic nuclear bulge, because all stars are believed to born in star clusters.

Hyper velocity star

There are some stars whose velocity is too fast, hyper velocity stars, to be explained with the normal star formation process. One of promising origins of the hypervelocity stars is a population kicked out from the strong gravitational influence of the SMBH in the Galactic center. If JASMINE found such hyper velocity stars to be consistent with this scenario in the Galactic center, it provides a direct evidence of the SMBH origin of hyper velocity stars.

Astrometric gravitational microlensing

Astrometric gravitational microlensing is a phenomenon that the position of a background star changes when a compact object, such as a stellar mass black hole, passed through between the background stars and us. JASMINE will monitor such microlensing events, which will tell us the number and masses of black holes.

Exoplanets (Photometric Transit)

JASMINE will make the targeted observations for the other sciences, on which unique capability of JASMINE can provide strong impact, in summer and winter when the Galactic center is not observable. The selection of the target is on-going. The candidates are listed below.

Exoplanets (Extrasolar Planets)

Planets around a star can gravitationally attract the host star, and the position of the star in the sky slightly shifts depending on the relative positions of the planets. This can be observed as periodic positional shifts, and enables us to find new exoplanets using astrometry. Exoplanets can be found with the transits seen in the light curve of the host star, i.e. the periodic dimming of the stellar light when a planet passes the front of the star. JASMINE especially targets M-type main-sequence stars, which is a low temperature low mass star, but bright in near-infrared. Because M-type main-sequence stars are intrinsically less bright, the so-called habitable zone of the planet, where the life is likely to be able to survive, is closer to the star and therefore the orbital period of habitable planets is short. Therefore, M-type main-sequence stars are the ideal target to discover a habitable planet. JASMINE can provide time-series near-infrared photometry for M-type main sequence stars, and therefore JASMINE is an ideal satellite to detect habitable planets around M-type main-sequence stars.

Other potential targets

Compact objects, e.g. Cygnus X-1. Variable stars. Star forming regions.

The Mission

Overview

• Launch Vehicle: Epsilon Rocket/JAXA
• Orbit: Sun-Synchronous
• Altitude: >550km
• Lifetime: 3 years
• Mass of satellite: about 400kg
• Telescope: aperture size ~ 30cm
• Detector: one 4K x 4K HgCdTe array or nine 1.3K x 1.3K InGaAs IR arrays
• Wavelength: 1.1 ~ 1.7um or 1.1 ~ 1.6um

Technical Challenges

Astrometric observations in space

• Space observations are required, because of no atmospheric turbulence and no atmospheric absorption.
• Observation at Low Earth Orbit --> Orbital period is ~100 minutes.
• Extreme thermal conditions.
• The Galactic center is only observable in spring and autumn, to avoid pointing the telescope toward the Sun.

Ultra-stable telescope

• Extremely low thermal expansion material for the satellite structure.
• Extremely low thermal expansion ceramic mirrors.
• Precise thermal control for a detector module.

Innovative data analysis technique

• A large number of repeat observations of the Galactic Center region.
• Achieving the precise measurements of the position of stars from a large number of the images.
• Determining the annual parallax and proper motion of the stars from three-year observational data.

Collaboration

International Supports

• JASMINE is the first NIR astrometry mission and a unique project. There is no other similar mission proposal in the 2020s and 2030s.
• Recommended by An International Committee: JASMINE received the IAU Commission A1 (international astrometry community) recommendation.
• Collaboration with the international astrometry community:JASMINE is closely collaborating with the Gaia data analysis consortium and the astrometry department of the US Naval Observatory.

Domestic Supports

• 2018: Recommended by Group of Optical and Infrared Astronomers (GOPIRA), as an ambitious mission for the first NIR astrometric observation in space, and as the most impactful mission for exploring the Galactic Center.
• March 2018: Recommended to be in the list of "MASTER PLAN 2020" (next future planning) of Science Council of Japan.

Institutes

• National Astronomical Observatory of Japan (NAOJ)
  • "Scientific Goals and Missions - JASMINE Project/NOAJ" [here]
• Kyoto University
• Institute of Space and Astronautical Science (ISAS), JAXA
• University College London, UK
• Niigata University
• The University of Tokyo
• Heidelberg University, Germany
• The United States Naval Observatory (USNO), US
• etc.