MAVEN-based investigation of Martian exobase temperatures: Diurnal and solar cycle variations
-
摘要: 火星逃逸面是理解其大气逃逸和演化过程的一个关键性概念. 本文基于搭载在火星大气与挥发分演化（MAVEN）卫星上的中性气体与离子质谱仪测量的中性成分密度数据，计算了火星大气中四种含量最多的成分（即CO2、O、N2和 CO）的逃逸面温度. 计算结果显示这四种成分的逃逸面温度具有较强的变化性，对应平均值分别为174 K、152 K、195 K和193 K. 计算出的四种成分的逃逸面温度均与其逃逸面高度成正相关而与其逃逸面密度成反相关. 进一步的研究表明逃逸面温度具有很强的日变化和太阳活动性变化：（1）火星日侧逃逸面温度高于夜侧，14时到达最高值，2时到达最低值；（2）火星逃逸面温度随太阳极紫外辐射的增加而增加，这一效果在日侧更加显著. 这些变化性是由不同的太阳极紫外波段的辐射能量注入对火星高层大气的不同加热程度导致的.Abstract: The exobase is a key concept for understanding atmospheric escape and evolution on Mars. With the aid of neutral density data measured via the Neutral Gas and Ion Mass Spectrometer onboard the Mars Atmosphere and Volatile Evolution spacecraft, we calculated the exobase temperatures of four relatively abundant species on Mars: CO2, O, N2, and CO. Our calculations revealed that the exobase temperatures are highly variable, with median temperatures of 174, 152, 195, and 193 K for CO2, O, N2, and CO, respectively. Moreover, the calculated exobase temperatures for the four species increased systematically with an increase in the exobase altitude or a decrease in the exobase density. Further investigations indicated strong diurnal and solar cycle variations in the exobase temperature: (1) the exobase temperature on the day side was higher than that on the night side, revealing a maximum temperature near the local time of 14 h and a minimum temperature near the local time of 2 h; and (2) the exobase temperatures of the four species increased with the solar extreme ultraviolet (EUV) flux, a feature that was restricted to the day side and absent on the night side, where non-solar energy inputs are likely important. These variations originate from the varying degrees of upper atmospheric heating on Mars in response to the different solar EUV energy inputs.
-
Key words:
- Mars /
- atmospheric escape /
- exobase
-
Figure 1. (a) Sample distribution with respect to Martian local time and integrated solar flux at 0.5～90 nm, referred to as the CO2 exobase altitude, both as a function of the MAVEN orbit number. The observations used in this study spanned three Marian years, from MY32 to MY34, as indicated in the figure legend; (b) Global distribution of the MAVEN observations used in this study with respect to the longitude and latitude, also referred to as the CO2 exobase altitude
Figure 2. Exobase temperatures of CO2, O, N2, and CO as a function of the exobase altitude on Mars. The black dashed lines indicate the median trends along with the standard deviations within the predefined altitude bins, whereas the red solid stars correspond to the median exobase altitude and temperature of all MAVEN measurements considered in this study
Figure 3. Similar to Fig. 2 but for exobase temperatures of CO2, O, N2, and CO as a function of the exobase density on Mars
Figure 4. Similar to Fig. 2 but for exobase temperatures of CO2, O, N2, and CO as a function of the Martian local time
Figure 5. Exobase temperatures of CO2, O, N2, and CO on the day side (red dots) and night side (blue dots) as a function of the integrated solar flux at 0.5～90 nm on Mars. The black dashed lines represent the median trend along with the standard deviations within the predefined integrated solar flux bins
-
[1] Angelats i Coll M, Forget F, López-Valverde M A, et al. 2004. Upper atmosphere of Mars up to 120 km: Mars Global Surveyor accelerometer data analysis with the LMD general circulation model[J]. Journal of Geophysical Research: Planets, 109(E1): E01011. [2] Bertaux J L, Korablev O, Perrier S, et al. 2006. SPICAM on Mars Express: Observing modes and overview of UV spectrometer data and scientific results[J]. Journal of Geophysical Research: Planets, 111(E10): E10S90. [3] Bougher S W, McDunn T M, Zoldak K A, et al. 2009. Solar cycle variability of Mars dayside exospheric temperatures: Model evaluation of underlying thermal balances[J]. Geophysical Research Letters, 36(5): L05201. [4] Bougher S W, Jakosky B, Halekas J, et al. 2015. Early MAVEN Deep Dip campaign reveals thermosphere and ionosphere variability[J]. Science, 350(6261): 0459. [5] Bougher S W, Roeten K J, Olsen K, et al. 2017. The structure and variability of Mars dayside thermosphere from MAVEN NGIMS and IUVS measurements: Seasonal and solar activity trends in scale heights and temperatures[J]. Journal of Geophysical Research:Space Physics, 122(1): 1296-1313. doi: 10.1002/2016JA023454 [6] Chaffin M S, Chaufray J Y, Stewart I, et al. 2014. Unexpected variability of Martian hydrogen escape[J]. Geophysical Research Letters, 41(2): 314-320. doi: 10.1002/2013GL058578 [7] Chamberlain J W. 1963. Planetary coronae and atmospheric evaporation[J]. Planetary and Space Science, 11(8): 901-960. doi: 10.1016/0032-0633(63)90122-3 [8] Chaufray J Y. 2021. Departure of the thermal escape rate from the jeans escape rate for atomic hydrogen at Earth, Mars, and Pluto[J]. Planetary and Space Science, 198: 105178. doi: 10.1016/j.pss.2021.105178 [9] Cui J, Yelle R V, Zhao L L, et al. 2018. The impact of crustal magnetic fields on the thermal structure of the Martian upper atmosphere[J]. The Astrophysical Journal Letters, 853(2): L33. doi: 10.3847/2041-8213/aaa89a [10] Cui J, Ren Z P, Wu Z P, et al. 2020. Abnormal dawn-dusk asymmetry of protonated ions in the Martian ionosphere[J]. The Astrophysical Journal Letters, 895(2): L43. doi: 10.3847/2041-8213/ab930c [11] England S L, Liu G, Yiǧit E, et al. 2017. MAVEN NGIMS observations of atmospheric gravity waves in the Martian thermosphere[J]. Journal of Geophysical Research: Space Physics, 122(2): 2310-2335. doi: 10.1002/2016JA023475 [12] Forbes J M, Lemoine F G, Bruinsma S L, et al. 2008. Solar flux variability of Mars' exosphere densities and temperatures[J]. Geophysical Research Letters, 35(1): L01201. [13] Forget F, Montmessin F, Bertaux J L, et al. 2009. Density and temperatures of the upper Martian atmosphere measured by stellar occultations with Mars Express SPICAM[J]. Journal of Geophysical Research: Planets, 114(E1): E01004. [14] Fu M, Cui J, Wu X, et al. 2020. The variations of the Martian exobase altitude[J]. Earth and Planetary Physics, 4(1): 4-10. [15] Gu H, Cui J, Niu D D, et al. 2020. Neutral heating efficiency in the dayside Martian upper atmosphere[J]. The Astronomical Journal, 159(2): 39. doi: 10.3847/1538-3881/ab5fcc [16] Gupta N, Venkateswara Rao N, Kadhane U R. 2019. Dawn-dusk asymmetries in the Martian upper atmosphere[J]. Journal of Geophysical Research: Planets, 124(12): 3219-3230. doi: 10.1029/2019JE006151 [17] Jakosky B M, Lin R P, Grebowsky J M, et al. 2015. The Mars atmosphere and volatile evolution (MAVEN) mission[J]. Space Science Reviews, 195(1-4): 3-48. doi: 10.1007/s11214-015-0139-x [18] Jakosky B M, Brain D, Chaffin M, et al. 2018. Loss of the Martian atmosphere to space: Present-day loss rates determined from MAVEN observations and integrated loss through time[J]. Icarus, 315: 146-157. doi: 10.1016/j.icarus.2018.05.030 [19] Johnson R E, Combi M R, Fox J L, et al. 2008. Exospheres and atmospheric escape[J]. Space Science Reviews, 139(1-4): 355-397. doi: 10.1007/s11214-008-9415-3 [20] Lammer H, Chassefière E, Karatekin Ö, et al. 2013. Outgassing history and escape of the Martian atmosphere and water inventory[J]. Space Science Reviews, 174(1-4): 113-154. doi: 10.1007/s11214-012-9943-8 [21] Lillis R J, Brain D A, Bougher S W, et al. 2015. Characterizing atmospheric escape from Mars today and through time, with MAVEN[J]. Space Science Reviews, 195(1-4): 357-422. doi: 10.1007/s11214-015-0165-8 [22] Lillis R J, Deighan J, Fox J L, et al. 2017. Photochemical escape of oxygen from Mars: First results from MAVEN in situ data[J]. Journal of Geophysical Research: Space Physics, 122(3): 3815-3836. doi: 10.1002/2016JA023525 [23] López-Valverde M A, Gerard J C, González-Galindo F, et al. 2018. Investigations of the Mars upper atmosphere with ExoMars trace gas orbiter[J]. Space Science Reviews, 214(1): 29. doi: 10.1007/s11214-017-0463-4 [24] Mahaffy P R, Benna M, King T, et al. 2015a. The neutral gas and ion mass spectrometer on the Mars atmosphere and volatile evolution mission[J]. Space Science Reviews, 195(1-4): 49-73. doi: 10.1007/s11214-014-0091-1 [25] Mahaffy P R, Benna M, Elrod M, et al. 2015b. Structure and composition of the neutral upper atmosphere of Mars from the MAVEN NGIMS investigation[J]. Geophysical Research Letters, 42(21): 8951-8957. doi: 10.1002/2015GL065329 [26] Nier A O, McElroy M B. 1976. Structure of the neutral upper atmosphere of Mars: Results from Viking 1 and Viking 2[J]. Science, 194(4271): 1298-1300. doi: 10.1126/science.194.4271.1298 [27] Nier A O, McElroy M B. 1977. Composition and structure of Mars' upper atmosphere: Results from the neutral mass spectrometers on Viking 1 and 2[J]. Journal of Geophysical Research, 82(B28): 4341-4350. [28] Niu D D, Cui J, Gu H, et al. 2021. In situ heating of the nightside Martian upper atmosphere and ionosphere: The role of solar wind electron precipitation[J]. The Astrophysical Journal, 909(2): 108. doi: 10.3847/1538-4357/abdbb0 [29] Qin J. 2020. Mars upper atmospheric Temperature and atomic oxygen density derived from the O I 130.4 nm emission observed by NASA's MAVEN mission[J]. The Astronomical Journal, 159(5): 206. doi: 10.3847/1538-3881/ab7fae [30] Qin J. 2021. Solar cycle, seasonal, and dust-storm-driven variations of the Mars upper atmospheric state and H escape rate derived from the Lyα emission observed by NASA's MAVEN mission[J]. The Astrophysical Journal, 912(1): 77. doi: 10.3847/1538-4357/abed4f [31] Siddle A G, Mueller-Wodarg I C F, Stone S W, et al. 2019. Global characteristics of gravity waves in the upper atmosphere of Mars as measured by MAVEN/NGIMS[J]. Icarus, 333: 12-21. doi: 10.1016/j.icarus.2019.05.021 [32] Slipski M, Jakosky B M, Benna M, et al. 2018. Variability of Martian turbopause altitudes[J]. Journal of Geophysical Research: Planets, 123(11): 2939-2957. doi: 10.1029/2018JE005704 [33] Stone S W, Yelle R V, Benna M, et al. 2018. Thermal structure of the Martian upper atmosphere from MAVEN NGIMS[J]. Journal of Geophysical Research: Planets, 123(11): 2842-2867. doi: 10.1029/2018JE005559 [34] Thiemann E M B, Chamberlin P C, Eparvier F G, et al. 2017. The MAVEN EUVM model of solar spectral irradiance variability at Mars: Algorithms and results[J]. Journal of Geophysical Research:Space Physics, 122(3): 2748-2767. doi: 10.1002/2016JA023512 [35] Withers P. 2006. Mars Global Surveyor and Mars Odyssey Accelerometer observations of the Martian upper atmosphere during aerobraking[J]. Geophysical Research Letters, 33(2): L02201. -
下载:
点击查看大图
图(5)
计量
- 文章访问数: 352
- HTML全文浏览量: 199
- PDF下载量: 76
- 被引次数: 0
