The Earth 2.0 (ET) space mission has entered its phase B study in China. It seeks to understand how frequently habitable Earth-like planets orbit solar-type stars (Earth 2.0s), the formation and evolution of terrestrial-like planets, and the origin of free-floating planets. The final design of ET includes six 28 cm diameter transit telescope systems, each with a field of view of 550 square degrees, and one 35 cm diameter microlensing telescope with a field of view of 4 square degrees. In transit mode, ET will continuously monitor over 2 million FGKM dwarfs in the original Kepler field and its neighboring fields for four years. Simultaneously, in microlensing mode, it will observe over 30 million I < 20.5 stars in the Galactic bulge direction. Simulations indicate that ET mission could identify approximately 40,000 new planets, including about 4,000 terrestrial-like planets across a wide range of orbital periods and in the interstellar space, ~1000 microlensing planets, ~10 Earth 2.0s and around 25 free-floating Earth mass planets. Coordinated observations with ground-based KMTNet telescopes will enable the measurement of masses for ~300 microlensing planets, helping determine the mass distribution functions of free-floating planets and cold planets. ET will operate from the Earth-Sun L2 halo orbit with a designed lifetime exceeding 4 years. The phase B study involves detailed design and engineering development of the transit and microlensing telescopes. Updates on this mission study are reported.
Earth2.0 is a space telescope mission proposed by Chinese scientists to search for exoplanets. It is scheduled for launch in 2027 and will operate in orbit around the Earth-Sun Lagrange point L2 for a minimum of 4 years. The mission includes six 28cm aperture, 550 square degree transit telescopes and one 35cm aperture, 4 square degree microlensing telescope. The microlensing telescope is aimed at the core area of the Milky Way's arm, and is expected to discover approximately 1,000 cold and wandering planets within four years. Currently, the microlensing telescope is considering using Teledyne e2v's CCD290 as the detector, with a focal plane consisting of a 2*2 detector mosaic. To conduct preliminary technical verification, a CCD290 prototype camera was designed and CCD290 performance characterization tests were carried out. Additionally, specific experiments were conducted to study the impact of space radiationontheCCD290 detector's performance through proton displacement damage irradiation. Following cumulative doses of3.072*10 10 p/cm2 and 6.792*10 10 p/cm2 of 60MeV proton irradiation, dark current, dark current non-uniformity, and charge transfer efficiency tests were performed on the CCD290. The test results indicated that after annealing at room temperature for 4 days and at 50°C for 7 days, the CCD performance showed partial restoration, highlighting the necessity of regular annealing in orbit.
To detect exoplanets and study their formation and evolution, several exoplanet space missions, such as Kepler, TESS, GAIA, and CHEOPS, have been successfully developed and fully operated in space. However, China has not yet had its own exoplanet space mission. The Earth 2.0 (ET) space mission is being developed in China aiming at detecting and characterizing exoplanets, especially extra-terrestrial like planets. ET will carry six transit telescopes pointing to the same sky region and a gravitational microlensing telescope, with the goal of finding habitable Earth like planets (Earth 2.0s) around solar type stars and measure its occurrence rate. In order to detect Earth 2.0s, ultrahigh-precision photometry of ∼30 ppm is required, which places tight constrain on camera performance, such as high-speed readout, low readout noise, mosaic detectors, and radiation tolerance. As of now, a prototype camera utilizing a CCD250-82 detector from Teledyne e2v has been developed and its performance has been tested. At a readout rate of 2 M pixels/s, the readout noise of 10.96 e− RMS and the pixel response nonuniformity of 0.66% at 600 nm have been achieved. After receiving radiation doses of 5 krad (Si) and 13.43 krad (Si), the dark current of the CCD increased by 30% and 126%, respectively. The camera’s key performance meets the basic requirements for the ET space mission, except for its high cooling power consumption.
We present an overview of the photometry simulation software developed for the Earth 2.0 (ET) mission. This software provides insights into the consequences of pre-production survey design choices by providing simulated pixel data required for photometric analysis. Validation of the simulation has been accomplished through comparison of simulated and real light curve data, reproducing Kepler’s light curves with combined photometric precision within 5 ppm of that measured in the real data. Large-scale noise component analysis on thousands of simulated stars is also in close agreement with those reported by the Kepler mission. Simulation results for ET show that the current design allows for a photometric precision of 34 ppm for 13th Kp magnitude solar-type stars when using a 6.5 hr integration.
A space mission called “Earth 2.0 (ET)” is being developed in China to address a few of fundamental questions in the exoplanet field: How frequently habitable Earth-like planets orbit solar type stars (Earth 2.0s)? How do terrestrial planets form and evolve? Where did floating planets come from? ET consists of six 30 cm diameter transit telescope systems with each field of view of 500 square degrees and one 35 cm diameter microlensing telescope with a field of view of 4 square degrees. The ET transit mode will monitor ~1.2M FGKM dwarfs in the original Kepler field and its neighboring fields continuously for four years while the microlensing mode monitors over 30M I< 20.6 stars in the Galactic bulge direction. ET will merge its photometry data with that from Kepler to increase the time baseline to 8 years. This enhances the transit signal-to-noise ratio, reduce false positives, and greatly increases the chance to discover Earth 2.0s. Simulations show that ET transit telescopes will be able to identify ~17 Earth 2.0s, about 4,900 Earth-sized terrestrial planets and about 29,000 new planets. In addition, ET will detect about 2,000 transit-timingvariation (TTV) planets and 700 of them will have mass and eccentricity measurements. The ET microlensing telescope will be able to identify over 1,000 microlensing planets. With simultaneous observations with the ground-based KMTNet telescopes, ET will be able to measure masses of over 300 microlensing planets and determine the mass distribution functions of free-floating planets and cold planets. ET will be operated at the Earth-Sun L2 orbit with a designed lifetime longer than 4 years.
The Earth 2.0 (ET) mission is a Chinese next-generation space mission aiming at detecting thousands of terrestrial-like planets, including habitable Earth-like planets orbiting solar type stars (i.e., Earth’s 2.0s), cold low-mass planets, and free-floating planets. The ET mission will use six 300 mm diameter wide field telescope arrays to continuously monitor 1.2 million FGKM dwarf stars in the original Kepler field and its adjacent regions for four consecutive years to search for new planets including Earth 2.0s using the transit technique. The six telescopes have the same configuration, point to the same sky area, and constitute the main scientific payload. Each telescope has an effective aperture of 300 mm with a very wide field of view (FOV) of 500 square degrees and a wavelength coverage of 450-900 nm. Each telescope is equipped with a focal plane mosaic camera. The mosaic camera is composed of 2×2, 9k×9k CMOS detectors with pixel size of 10μm. The optical design results in the diameter of the 90% encircled energy (EE90%) less than 40μm (or 4 pixels) over the entire FOV. About 20% vignetting at the edge of the FOV is introduced to provide good throughput for the entire FOV while keeping optics size and weight down to reduce manufacturing risk and scientific payload within the mass and volume limit. In this paper, we will present the optical design details, including influence analysis of various factors on image quality, e.g., glass material, detector flatness, manufacturing and assembly tolerances. In addition, we will describe temperature stability analysis of the telescope on image quality and photometry measurements.
The Earth 2.0 (ET) mission is a Chinese space mission to detect thousands of Earth-sized terrestrial planets, including habitable Earth-like planets orbiting solar type stars (Earth 2.0s), cold low-mass planets, and free-floating planets. The six 30 cm diameter transit telescopes will be equipped with a CMOS camera which consists of 4(2×2)9K×9K CMOS sensors. A prototype camera with a 8900×9120 pixel GSENSE 1081 BSI type CMOS sensor and temperature control is designed and developed for high precision photometry measurements. In this paper, details of this camera design and performance test results are reported.
KEYWORDS: Planets, Data processing, Charge-coupled devices, Signal processing, Exoplanets, Databases, Calibration, Space operations, Smoothing, Signal to noise ratio
We present an overview of the data processing pipeline for the simulated data from the Earth 2.0 (ET) mission which is being developed in China. Our pipeline contains several modules, similar to the pipelines of some existing space missions aiming at exoplanet detection. The pipeline includes 1). the Pixel Level Calibration (PLC) module (such as bias correction, nonlinearity correction, undershoot correction, and flat correction); 2). the Photometric Analysis (PA) module; 3). the Presearch Data Conditioning (PDC) module (such as flux discontinuity correction, systematic error correction, and light curve flatten); 4). the Transiting Planet Search (TPS) module; 5). the Parameters Fitting (PF) module. Since we have not decided whether to use CCD or CMOS as the ET detector, we have prepared two versions of pipelines, respectively. We have used the existing Kepler raw pixel data to validate the pipeline in the CCD version, and the pipeline has successfully detected known transiting planet signals with similar S/N. In addition, our fitted parameters are highly consistent with those published parameters within a 1% to 10% difference (such as orbital period, orbital inclination, semi-major axis, and planetary radius). This pipeline is still in preliminary development. In the future, we will improve the running speed, detection accuracy and completeness by incorporating the deep learning technique and corrections of instrumental effects (such as the thermal effect and guiding errors). Eventually, the output of our pipeline will be used to feedback to ET mission design to maximize its science output.
The Earth 2.0 (ET) mission is a Chinese space mission designed to detect thousands of terrestrial-like planets, including habitable Earth-like planets orbiting solar type stars (i.e., Earth 2.0s), cold low-mass planets, and free-floating planets. Six 30cm telescopes are used for very high precision photometry measurements to detect transiting planets. In order to reach very high precision photometry, an intra-pixel response function (IPRF) of detectors needs to be measured for the ET design to keep image motions caused by spacecraft operation within an acceptable level. To characterize detectors, two setups have been developed in the lab to measure spot size of the characterization beam and subpixel sensitivity. Early characterization results are reported.
An innovative Chinese space mission, the Earth 2.0 (ET) mission, is being developed to combine the transit and microlensing method together to search for Earth-sized exoplanets in the Galaxy, including the most precious ones—Earth 2.0s, i.e., habitable Earth-sized (0.8-1.25 Earth radii) planets orbiting solar type stars, cold and free-floating low-mass planets. ET’s 6 transit telescopes will monitor a FoV of 500 square degrees (covering the Kepler field) continuously for at least four years and generate a huge database containing high-cadence and ultra-high photometry precision light curves of 1.2 million FGKM dwarfs. With such a high value database in hand, many unsolved issues in the exoplanet field and even stellar sciences will be well addressed. Besides looking for Earth 2.0s and constraining its occurrence rate, ET will be dedicated to map a much wider radius-period diagram of terrestrial-like exoplanets than ever and reveal how it depends on the stellar properties and environments. With the 4-yr legacy data of Kepler, ET will observe some planet systems for up to 8 years and catch additional components in a multi-planet system, e.g. cold Giant, cold sub-Earths, exomoons, exorings and even exocomets. Are exomoons and exocomets common in a planet system? What’s the favorite number of planets in a multi-planet system? What’s the most common orbital configuration of planet systems? With these new data, ET will deepen our understandings on how unique our Solar system is and how do multi-planet systems evolve. In addition to exoplanet sciences, ET’s time series data will also benefit the studies in asteroseismology, archeology in the Galaxy, time-domain astrophysics and black hole science.
The Earth 2.0 (ET) mission is a Chinese next generation space mission designed to find thousands of terrestrial-like planets including habitable Earth-like planets orbiting solar type stars (Earth 2.0s) through the transiting method, and cold and free-floating low-mass planets through the microlensing method. The mission will monitor 1.2M FGKM dwarf stars for patterns of transits with a differential photometry precision of 34 ppm for a G = 13.5 mag solar type star in a 6.5-hr exposure. ET will be operated at the Earth-Sun L2 halo orbit with a designed lifetime longer than 4 years. To increase the probability of discovering Earth 2.0s, wide field-of-view (FoV) and ultra-high photometry precision are two key features of this mission. The wide field transiting telescope design offers 500 square degrees of FOV. High photometry precision is achieved by the scientific payload design as well as high stable spacecraft pointing in both short term (jitters) and long-term (drifts). According to our photometry simulations and analysis, the ET spacecraft stability requirement is not the usual relative pointing error (RPE) applied in most space missions, but the forward sum stability, in which both high frequency jitters and low frequency drifts are critical for high precision photometry measurements. Therefore, the spacecraft design needs to not only deal with high frequency jitters, but also the thermal-elastic effects of scientific payloads, including long-term thermal stability of the telescope structure, cameras, fine guiding camera, and mounting plate. This paper presents the pointing stability definition suitable for the ET mission. Simulations of high precision photometry observations with different pointing stability scenarios are presented. Approaches to the high stability are also discussed.
The Earth 2.0 (ET) mission is a Chinese next-generation space mission to detect thousands of Earth-sized terrestrial planets, including habitable Earth-like planets orbiting solar type stars (Earth 2.0s), cold low-mass planets, and freefloating planets. To meet the scientific goals, the ET spacecraft will carry six 30 cm diameter transit telescopes with each field of view of 500 square degrees, and one 35 cm diameter microlensing telescope with a field of view of 4 square degrees, monitor ~1.2M FGKM dwarfs in the original Kepler field and its neighboring fields continuously while monitoring over 30M stars in the Galactic bulge direction. The high precision transit observations require high photometry precision and pointing stability, which is the key drive for the ET spacecraft design. In this paper, details of the overall mission modeling and analysis will be presented. The spacecraft orbit, pointing strategy, stability requirements are presented, as well as the space-ground communication analysis. The ET spacecraft adopts an ultra-high photometry precision & high stable platform, largely inherited from other space science missions. The preliminary design of spacecraft which meets mission requirements is introduced, including the spacecraft overall configuration, observation modes, avionics architecture and development plan, which pays great attention to the pointing stability and huge volume science telemetry download.
Earth 2.0 is a Chinese space satellite mission that uses the transit and microlensing methods to search for exoplanets, especially Earth-sized terrestrial planets, including habitable terrestrial planets around sun-like stars. The satellite will work in the halo orbit of the Sun-Earth L2 point for at least 4 years, and is expected to find about 20 Earth like planets in the 4-year observation period. In this paper a CCD camera prototype based on a 4kx4k CCD250 detector for early technology demonstration and high-accuracy photometric performance verification is introduced. The key performance indicators such as readout noise, gain, and linearity of the camera are tested, and the test results will be described.
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