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.
Quasar absorption lines (QALs), created by the light of celestial objects billions of light-years away, can be used to trace gas components from distant galaxies and thus are crucial to the study of galaxy evolution. Ca II QALs, in particular, are important for studying both star formation and recent galaxies because they are one of the dustiest QALs and are located at lower redshifts. However, Ca II QALs are quite difficult to detect, so the number of known Ca II QALs is extremely low, leaving many important models and theories unconfirmed. In this work, we developed an accurate and efficient approach to search for Ca II QALs using deep learning. We created large amount of simulation data for our training set, while we used an existing Ca II QAL catalog for our test set. We also designed a novel preprocessing method aimed at discovering weak Ca II absorption lines. Our solution achieved an accuracy of 96% on the test dataset and runs thousands of times faster than traditional methods. Our trained neural network model was applied to quasar spectra from the Sloan Digital Sky Survey’s Data Releases 7, 12, and 14, and discovered 542 brand-new Ca II QALs and. This is currently the largest catalog of Ca II QALs ever discovered, which will play a significant role in creating new theories and confirming existing theories. Furthermore, our approach can be applied to the search of virtually any other type of QAL, opening up opportunities for ground-breaking research about galaxy evolution.
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.
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.
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.
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 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.
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