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笔记｜天文数据科学03｜机器学习甄别系外行星

2026-07-09

理工研习

Python

/

数据科学

/

天文学

在前两篇文章中，我们通过肉眼和 BLS 算法分析了单颗恒星的光变曲线。但在真实的 Kepler 任务中，望远镜发现了数千个候选信号——其中许多是假阳性（如食双星、仪器噪声等）。

本文的目标是：利用 Pandas DataFrame 组织大规模候选体数据，训练一个随机森林分类器，让机器学习模型自动甄别真实的系外行星。

1. DataFrame 热身练习#

1.1 创建玩具数据集#

用三个模拟的系外行星候选体数据来熟悉 DataFrame 的基本操作。每条记录包含周期、凌星深度、持续时间、信噪比和文字描述：

1
import pandas as pd
2

3
warmup = pd.DataFrame([
4
    {
5
        "case": "A",
6
        "period_days": 3.2,
7
        "depth_percent": 0.8,
8
        "duration_hours": 2.1,
9
        "snr": 14.0,
10
        "description": "regular repeated U-shaped dips"
11
    },
12
    {
13
        "case": "B",
14
        "period_days": 8.5,
15
        "depth_percent": 0.1,
16
        "duration_hours": 1.0,
17
        "snr": 2.2,
18
        "description": "weak messy signal, not clearly repeating"
19
    },
20
    {
21
        "case": "C",
22
        "period_days": 1.7,
23
        "depth_percent": 8.5,
24
        "duration_hours": 6.0,
25
        "snr": 20.0,
26
        "description": "very deep V-shaped repeated dips"
27
    },
28
])
29

30
warmup

输出：

1
  case  period_days  depth_percent  duration_hours   snr  \
2
0    A          3.2            0.8             2.1  14.0
3
1    B          8.5            0.1             1.0   2.2
4
2    C          1.7            8.5             6.0  20.0
5

6
                                description
7
0            regular repeated U-shaped dips
8
1  weak messy signal, not clearly repeating
9
2          very deep V-shaped repeated dips

1.2 添加新列#

为每个案例添加人工标注的分类标签。在天文学中，常见的分类包括：

candidate_like：类似真实行星候选体（U 形凹陷、高 SNR、周期性）
weak_or_noise：信号太弱或噪声（低 SNR、无清晰重复）
possible_binary：可能是食双星（很深的 V 形凹陷）

1
toy_df = warmup.copy()
2

3
toy_df["human_label"] = [
4
    "candidate_like",
5
    "weak_or_noise",
6
    "possible_binary"
7
]
8

9
toy_df

输出：

1
  case  period_days  depth_percent  duration_hours   snr  \
2
0    A          3.2            0.8             2.1  14.0
3
1    B          8.5            0.1             1.0   2.2
4
2    C          1.7            8.5             6.0  20.0
5

6
                                description      human_label
7
0            regular repeated U-shaped dips   candidate_like
8
1  weak messy signal, not clearly repeating    weak_or_noise
9
2          very deep V-shaped repeated dips  possible_binary

1.3 DataFrame 基础属性#

1
print("Shape: ", toy_df.shape)
2
print('Rows:', toy_df.shape[0])
3
print('Columns:', toy_df.shape[1])

输出：

1
Shape:  (3, 7)
2
Rows: 3
3
Columns: 7

shape 返回 (行数, 列数) 元组。

1.4 列筛选#

选取特定列的子集。双层方括号 df[['col1', 'col2']] 返回 DataFrame，单层方括号 df['col'] 返回 Series：

1
toy_df[['case', 'period_days', 'depth_percent', 'snr']]

输出：

1
  case  period_days  depth_percent   snr
2
0    A          3.2            0.8  14.0
3
1    B          8.5            0.1   2.2
4
2    C          1.7            8.5  20.0

1.5 特征矩阵与标签向量#

在机器学习中，特征（Features）是输入模型的数值列，标签（Labels）是要预测的目标：

1
feature_columns = [
2
    'period_days',
3
    'depth_percent',
4
    'duration_hours',
5
    'snr'
6
]
7

8
toy_features = toy_df[feature_columns]
9
toy_features

输出：

1
   period_days  depth_percent  duration_hours   snr
2
0          3.2            0.8             2.1  14.0
3
1          8.5            0.1             1.0   2.2
4
2          1.7            8.5             6.0  20.0

1
toy_labels = toy_df['human_label']
2
toy_labels

输出：

1
0     candidate_like
2
1      weak_or_noise
3
2    possible_binary
4
Name: human_label, dtype: object

这就是监督学习的基本数据结构：X（特征矩阵） 和 y（标签向量）。

1.6 布尔条件筛选#

1
high_snr = toy_df[toy_df['snr'] > 5]
2
high_snr

输出：

1
  case  period_days  depth_percent  duration_hours   snr  \
2
0    A          3.2            0.8             2.1  14.0
3
2    C          1.7            8.5             6.0  20.0
4

5
                        description      human_label
6
0    regular repeated U-shaped dips   candidate_like
7
2  very deep V-shaped repeated dips  possible_binary

1
weak_signals = toy_df[toy_df['snr'] <= 5]
2
weak_signals

输出：

1
  case  period_days  depth_percent  duration_hours  snr  \
2
1    B          8.5            0.1             1.0  2.2
3

4
                                description    human_label
5
1  weak messy signal, not clearly repeating  weak_or_noise

1.7 多条件组合筛选#

用 &（与）和括号组合多个条件：

1
deep_signals = toy_df[toy_df['depth_percent'] > 2.0]
2
deep_signals

1
interesting = toy_df[
2
    (toy_df["snr"] > 5) &
3
    (toy_df["depth_percent"] < 5)
4
]
5

6
interesting

输出：

1
  case  period_days  depth_percent  duration_hours   snr  \
2
0    A          3.2            0.8             2.1  14.0
3

4
                      description     human_label
5
0  regular repeated U-shaped dips  candidate_like

这个查询找出了”高 SNR 但深度适中”的信号——最有可能是真实行星的候选体。

1.8 排序#

1
toy_df.sort_values("snr", ascending=False)

输出：

1
  case  period_days  depth_percent  duration_hours   snr  \
2
2    C          1.7            8.5             6.0  20.0
3
0    A          3.2            0.8             2.1  14.0
4
1    B          8.5            0.1             1.0   2.2
5

6
                                description      human_label
7
2          very deep V-shaped repeated dips  possible_binary
8
0            regular repeated U-shaped dips   candidate_like
9
1  weak messy signal, not clearly repeating    weak_or_noise

1
toy_df.sort_values("depth_percent", ascending=False)

1.9 值计数与布尔列#

1
toy_df["human_label"].value_counts()

输出：

1
human_label
2
candidate_like     1
3
weak_or_noise      1
4
possible_binary    1
5
Name: count, dtype: int64

创建布尔列作为派生特征：

1
toy_df["strong_signal"] = toy_df["snr"] >= 7
2

3
toy_df[["case", "snr", "strong_signal", "human_label"]]

输出：

1
  case   snr  strong_signal      human_label
2
0    A  14.0           True   candidate_like
3
1    B   2.2          False    weak_or_noise
4
2    C  20.0           True  possible_binary

1
toy_df["very_deep"] = toy_df["depth_percent"] > 5
2

3
toy_df[["case", "depth_percent", "very_deep", "human_label"]]

1.10 列运算与分组聚合#

创建派生数值列——简单评分 = SNR − 深度：

1
toy_df["simple_score"] = toy_df["snr"] - toy_df["depth_percent"]
2

3
toy_df[["case", "snr", "depth_percent", "simple_score", "human_label"]]

输出：

1
  case   snr  depth_percent  simple_score      human_label
2
0    A  14.0            0.8          13.2   candidate_like
3
1    B   2.2            0.1           2.1    weak_or_noise
4
2    C  20.0            8.5          11.5  possible_binary

按类别分组计算均值：

1
toy_df.groupby("human_label")[["period_days", "depth_percent", "duration_hours", "snr"]].mean()

输出：

1
                 period_days  depth_percent  duration_hours   snr
2
human_label
3
candidate_like           3.2            0.8             2.1  14.0
4
possible_binary          1.7            8.5             6.0  20.0
5
weak_or_noise            8.5            0.1             1.0   2.2

groupby("human_label").mean() 按分类标签分组后计算每个特征的平均值。可以看到：candidate_like 类具有适中的深度和较高的 SNR，而 possible_binary 类深度很大。

1.11 准备机器学习数据结构#

1
X_toy = toy_df[feature_columns]
2
y_toy = toy_df["human_label"]
3

4
print("X shape:", X_toy.shape)
5
print("y shape:", y_toy.shape)
6

7
display(X_toy)
8
display(y_toy)

输出：

1
X shape: (3, 4)
2
y shape: (3,)
3

4
   period_days  depth_percent  duration_hours   snr
5
0          3.2            0.8             2.1  14.0
6
1          8.5            0.1             1.0   2.2
7
2          1.7            8.5             6.0  20.0
8

9
0     candidate_like
10
1      weak_or_noise
11
2    possible_binary
12
Name: human_label, dtype: object

2. 大规模真实数据#

2.1 环境配置#

安装 scikit-learn 并导入所需库：

1
!pip -q install scikit-learn

1
import warnings
2
warnings.filterwarnings("ignore")
3

4
import numpy as np
5
import pandas as pd
6
import matplotlib.pyplot as plt
7

8
import requests
9
from io import StringIO
10
from IPython.display import display
11

12
from sklearn.model_selection import train_test_split
13
from sklearn.ensemble import RandomForestClassifier
14
from sklearn.metrics import (
15
    accuracy_score,
16
    precision_score,
17
    recall_score,
18
    classification_report,
19
    confusion_matrix,
20
    ConfusionMatrixDisplay,
21
)
22

23
RANDOM_STATE = 42
24

25
print("Libraries imported successfully.")
26
print("numpy:", np.__version__)
27
print("pandas:", pd.__version__)

输出：

1
Libraries imported successfully.
2
numpy: 2.3.5
3
pandas: 2.3.3

2.2 查询 NASA 系外行星数据库#

从 NASA Exoplanet Archive 下载 5000 条已知分类的记录——包括已确认行星（CONFIRMED）、候选体（CANDIDATE）和假阳性（FALSE POSITIVE）：

1
TAP_URL = "https://exoplanetarchive.ipac.caltech.edu/TAP/sync"
2

3
query = '''
4
select top 5000
5
    kepid,
6
    kepoi_name,
7
    kepler_name,
8
    koi_disposition,
9
    koi_period,
10
    koi_duration,
11
    koi_depth,
12
    koi_prad,
13
    koi_model_snr,
14
    koi_kepmag,
15
    koi_score
16
from cumulative
17
where koi_disposition in ('CONFIRMED', 'CANDIDATE', 'FALSE POSITIVE')
18
  and koi_period is not null
19
  and koi_duration is not null
20
  and koi_depth is not null
21
  and koi_prad is not null
22
  and koi_model_snr is not null
23
  and koi_kepmag is not null
24
'''

如果 NASA 查询失败，使用合成回退数据（make_fallback_archive 函数生成具有合理统计分布的人造数据）：

1
def make_fallback_archive(n_confirmed=120, n_fp=120, n_candidate=60, seed=42):
2
    # Create a small synthetic fallback table if the live NASA query fails.
3
    rng = np.random.default_rng(seed)
4

5
    rows = []
6

7
    def add_rows(n, disposition):
8
        for i in range(n):
9
            if disposition == "CONFIRMED":
10
                period = 10 ** rng.uniform(np.log10(0.8), np.log10(25))
11
                duration = rng.uniform(1.0, 8.0)
12
                depth = 10 ** rng.uniform(np.log10(200), np.log10(12000))
13
                prad = 10 ** rng.uniform(np.log10(0.8), np.log10(12))
14
                snr = 10 ** rng.uniform(np.log10(7), np.log10(80))
15
                kepmag = rng.uniform(10, 15)
16
            elif disposition == "FALSE POSITIVE":
17
                period = 10 ** rng.uniform(np.log10(0.3), np.log10(40))
18
                duration = rng.uniform(0.5, 16.0)
19
                depth = 10 ** rng.uniform(np.log10(1000), np.log10(100000))
20
                prad = 10 ** rng.uniform(np.log10(5), np.log10(80))
21
                snr = 10 ** rng.uniform(np.log10(3), np.log10(120))
22
                kepmag = rng.uniform(11, 16)
23
            else:
24
                period = 10 ** rng.uniform(np.log10(0.5), np.log10(35))
25
                duration = rng.uniform(0.7, 12.0)
26
                depth = 10 ** rng.uniform(np.log10(200), np.log10(50000))
27
                prad = 10 ** rng.uniform(np.log10(1), np.log10(35))
28
                snr = 10 ** rng.uniform(np.log10(4), np.log10(90))
29
                kepmag = rng.uniform(10, 16)
30

31
            rows.append({
32
                "kepid": int(10_000_000 + len(rows)),
33
                "kepoi_name": f"K{len(rows):05d}.01",
34
                "kepler_name": None if disposition != "CONFIRMED" else f"Kepler-{len(rows)} b",
35
                "koi_disposition": disposition,
36
                "koi_period": period,
37
                "koi_duration": duration,
38
                "koi_depth": depth,
39
                "koi_prad": prad,
40
                "koi_model_snr": snr,
41
                "koi_kepmag": kepmag,
42
                "koi_score": np.nan,
43
            })
44

45
    add_rows(n_confirmed, "CONFIRMED")
46
    add_rows(n_fp, "FALSE POSITIVE")
47
    add_rows(n_candidate, "CANDIDATE")
48

49
    return pd.DataFrame(rows)
50

51
archive_df = None
52

53
try:
54
    print("Querying NASA Exoplanet Archive...")
55
    response = requests.get(
56
        TAP_URL,
57
        params={"query": query, "format": "csv"},
58
        timeout=60,
59
    )
60
    response.raise_for_status()
61
    archive_df = pd.read_csv(StringIO(response.text))
62
    print("Live NASA rows downloaded:", len(archive_df))
63

64
except Exception as exc:
65
    print("NASA query failed. Using synthetic fallback data for the lesson.")
66
    print("Error:", exc)
67
    archive_df = make_fallback_archive()
68

69
print("Final table shape:", archive_df.shape)
70
archive_df.head()

输出：

1
Querying NASA Exoplanet Archive...
2
Live NASA rows downloaded: 5000
3
Final table shape: (5000, 11)
4

5
      kepid kepoi_name   kepler_name koi_disposition  koi_period  \
6
0  10797460  K00752.01  Kepler-227 b       CONFIRMED    9.488036
7
1  10797460  K00752.02  Kepler-227 c       CONFIRMED   54.418383
8
2  10811496  K00753.01           NaN       CANDIDATE   19.899140
9
3  10848459  K00754.01           NaN  FALSE POSITIVE    1.736952
10
4  10854555  K00755.01  Kepler-664 b       CONFIRMED    2.525592
11

12
   koi_duration  koi_depth  koi_prad  koi_model_snr  koi_kepmag  koi_score
13
0       2.95750      615.8      2.26           35.8      15.347      1.000
14
1       4.50700      874.8      2.83           25.8      15.347      0.969
15
2       1.78220    10829.0     14.60           76.3      15.436      0.000
16
3       2.40641     8079.2     33.46          505.6      15.597      0.000
17
4       1.65450      603.3      2.75           40.9      15.509      1.000

1
print('Columns:', list(archive_df.columns))

输出：

1
Columns: ['kepid', 'kepoi_name', 'kepler_name', 'koi_disposition', 'koi_period', 'koi_duration', 'koi_depth', 'koi_prad', 'koi_model_snr', 'koi_kepmag', 'koi_score']

3. 特征工程#

3.1 对数变换#

天文学数据通常是对数正态分布（数量级跨越很大）。取对数后数据更接近正态分布，模型训练效果更好：

1
def safe_log10(x):
2
    # Log10 transform that avoids problems with zero or negative values.
3
    x = pd.to_numeric(x, errors="coerce")
4
    return np.log10(np.clip(x, 1e-12, None))
5

6
features_df = archive_df.copy()
7

8
features_df["log_period"] = safe_log10(features_df["koi_period"])
9
features_df["log_duration"] = safe_log10(features_df["koi_duration"])
10
features_df["log_depth"] = safe_log10(features_df["koi_depth"])
11
features_df["log_prad"] = safe_log10(features_df["koi_prad"])
12
features_df["log_snr"] = safe_log10(features_df["koi_model_snr"])
13
features_df["kepmag"] = pd.to_numeric(features_df["koi_kepmag"], errors="coerce")
14

15
FEATURES = [
16
    "log_period",
17
    "log_duration",
18
    "log_depth",
19
    "log_prad",
20
    "log_snr",
21
    "kepmag",
22
]
23

24
features_df = features_df.dropna(subset=FEATURES + ["koi_disposition"]).copy()
25

26
print("Feature columns:", FEATURES)
27
features_df[["kepoi_name", "koi_disposition"] + FEATURES].head()

输出：

1
Feature columns: ['log_period', 'log_duration', 'log_depth', 'log_prad', 'log_snr', 'kepmag']
2

3
  kepoi_name koi_disposition  log_period  log_duration  log_depth  log_prad  \
4
0  K00752.01       CONFIRMED    0.977176      0.470925   2.789440  0.354108
5
1  K00752.02       CONFIRMED    1.735746      0.653888   2.941909  0.451786
6
2  K00753.01       CANDIDATE    1.298834      0.250956   4.034588  1.164353
7
3  K00754.01  FALSE POSITIVE    0.239788      0.381370   3.907368  1.524526
8
4  K00755.01       CONFIRMED    0.402363      0.218667   2.780533  0.439333
9

10
    log_snr  kepmag
11
0  1.553883  15.347
12
1  1.411620  15.347
13
2  1.882525  15.436
14
3  2.703807  15.597
15
4  1.611723  15.509

np.clip(x, 1e-12, None) 将所有 ≤0 的值替换为一个极小的正数（10⁻¹²），避免 log10(0) 或 log10(负数) 的数学错误。safe_log10 封装了这一安全处理。

3.2 划分训练集#

只使用已知标签的数据（CONFIRMED = 1，FALSE POSITIVE = 0）作为训练集，CANDIDATE 留作后续预测：

1
known_df = features_df[
2
    features_df["koi_disposition"].isin(["CONFIRMED", "FALSE POSITIVE"])
3
].copy()
4

5
candidate_df = features_df[
6
    features_df["koi_disposition"] == "CANDIDATE"
7
].copy()
8

9
known_df["label"] = (known_df["koi_disposition"] == "CONFIRMED").astype(int)
10

11
print("Known examples:", known_df.shape)
12
print("Candidate rows for later ranking:", candidate_df.shape)
13
print("\nLabel counts:")
14
print(known_df["label"].value_counts().rename(index={0: "false positive", 1: "confirmed"}))

输出：

1
Known examples: (4194, 18)
2
Candidate rows for later ranking: (806, 17)
3

4
Label counts:
5
label
6
confirmed         2526
7
false positive    1668
8
Name: count, dtype: int64

.astype(int) 将布尔值 True/False 转换为 1/0，这是机器学习中二分类标签的标准格式。

3.3 类别平衡#

如果确认行星（2526 个）远多于假阳性（1668 个），模型会偏向多数类。通过随机欠采样使两类数量相等：

1
confirmed = known_df[known_df["label"] == 1]
2
false_positive = known_df[known_df["label"] == 0]
3

4
n = min(len(confirmed), len(false_positive))
5

6
if n < 20:
7
    print("Warning: very few examples. The model will be only a toy demonstration.")
8

9
confirmed_bal = confirmed.sample(n=n, random_state=RANDOM_STATE)
10
false_positive_bal = false_positive.sample(n=n, random_state=RANDOM_STATE)
11

12
model_df = pd.concat([confirmed_bal, false_positive_bal], ignore_index=True)
13
model_df = model_df.sample(frac=1, random_state=RANDOM_STATE).reset_index(drop=True)
14

15
print("Balanced training table:", model_df.shape)
16
print(model_df["label"].value_counts().rename(index={0: "false positive", 1: "confirmed"}))
17

18
model_df[["kepoi_name", "koi_disposition"] + FEATURES + ["label"]].head()

输出：

1
Balanced training table: (3336, 18)
2
label
3
confirmed         1668
4
false positive    1668
5
Name: count, dtype: int64
6

7
  kepoi_name koi_disposition  log_period  log_duration  log_depth  log_prad  \
8
0  K01441.01       CONFIRMED    0.929775      0.468052   2.470557  0.278754
9
1  K03084.01  FALSE POSITIVE    0.187637      0.231215   2.029789 -0.036212
10
2  K00082.04       CONFIRMED    0.849503      0.440437   1.817565 -0.200659
11
3  K03279.01       CONFIRMED    1.488943      0.624695   2.807061  0.383815
12
4  K00351.01       CONFIRMED    2.520611      1.158483   3.920233  1.037028
13

14
    log_snr  kepmag  label
15
0  1.315970  15.135      1
16
1  1.082785  14.991      0
17
2  1.350248  11.492      1
18
3  1.143015  15.765      1
19
4  2.550228  13.804      1

pd.concat 拼接两个 DataFrame，sample(frac=1) 以 100% 比例打乱行顺序，reset_index(drop=True) 重置索引。

3.4 特征空间可视化#

以 log_depth 和 log_snr 为坐标轴，观察两类样本的分布：

1
plt.figure(figsize=(8, 5))
2

3
for label_value, label_name in [(1, "confirmed"), (0, "false positive")]:
4
    subset = model_df[model_df["label"] == label_value]
5
    plt.scatter(
6
        subset["log_depth"],
7
        subset["log_snr"],
8
        s=20,
9
        alpha=0.65,
10
        label=label_name,
11
    )
12

13
plt.xlabel("log10(transit depth [ppm])")
14
plt.ylabel("log10(model SNR)")
15
plt.title("Feature space: depth vs SNR")
16
plt.legend()
17
plt.grid(True)
18
plt.show()

已确认行星（蓝色）倾向于集中在特定的深度-SNR 区域，而假阳性（橙色）分布更分散——这为机器学习分类器提供了可学习的信息。

4. 训练随机森林分类器#

4.1 训练/测试拆分#

train_test_split 将数据随机分为训练集（75%）和测试集（25%），stratify=y 确保两个集合中类别比例一致：

1
X = model_df[FEATURES]
2
y = model_df["label"]
3

4
X_train, X_test, y_train, y_test, train_idx, test_idx = train_test_split(
5
    X,
6
    y,
7
    model_df.index,
8
    test_size=0.25,
9
    random_state=RANDOM_STATE,
10
    stratify=y,
11
)
12

13
print("Training examples:", len(X_train))
14
print("Test examples:", len(X_test))
15
print("\nTrain label counts:")
16
print(y_train.value_counts().rename(index={0: "false positive", 1: "confirmed"}))
17
print("\nTest label counts:")
18
print(y_test.value_counts().rename(index={0: "false positive", 1: "confirmed"}))

输出：

1
Training examples: 2502
2
Test examples: 834
3

4
Train label counts:
5
label
6
false positive    1251
7
confirmed         1251
8
Name: count, dtype: int64
9

10
Test label counts:
11
label
12
false positive    417
13
confirmed         417
14
Name: count, dtype: int64

4.2 训练模型#

随机森林（Random Forest）是多个决策树的集成，每棵树在数据的随机子集上训练。参数说明：

n_estimators=300：300 棵决策树
max_depth=5：每棵树最多 5 层（防止过拟合）
min_samples_leaf=3：叶节点最少 3 个样本
class_weight="balanced"：自动处理类别不平衡

1
model = RandomForestClassifier(
2
    n_estimators=300,
3
    max_depth=5,
4
    min_samples_leaf=3,
5
    random_state=RANDOM_STATE,
6
    class_weight="balanced",
7
)
8

9
model.fit(X_train, y_train)
10

11
print("Random Forest trained.")

输出：

1
Random Forest trained.

4.3 模型评估#

在测试集上评估模型性能：

准确率（Accuracy）：预测正确的比例
精确率（Precision）：预测为”确认行星”中真正是行星的比例
召回率（Recall）：真实行星中被正确找出的比例

1
y_pred = model.predict(X_test)
2
y_proba = model.predict_proba(X_test)[:, 1]
3

4
acc = accuracy_score(y_test, y_pred)
5
prec = precision_score(y_test, y_pred, zero_division=0)
6
rec = recall_score(y_test, y_pred, zero_division=0)
7

8
print("Test accuracy:", round(acc, 3))
9
print("Test precision:", round(prec, 3))
10
print("Test recall:", round(rec, 3))
11

12
print("\nClassification report:")
13
print(classification_report(
14
    y_test,
15
    y_pred,
16
    target_names=["false positive", "confirmed"],
17
    zero_division=0,
18
))

输出：

1
Test accuracy: 0.841
2
Test precision: 0.817
3
Test recall: 0.878
4

5
Classification report:
6
                precision    recall  f1-score   support
7

8
false positive       0.87      0.80      0.83       417
9
     confirmed       0.82      0.88      0.85       417
10

11
      accuracy                           0.84       834
12
     macro avg       0.84      0.84      0.84       834
13
  weighted avg       0.84      0.84      0.84       834

predict_proba 返回每个样本属于各类的概率，[:, 1] 取第二列（确认行星的概率）。模型整体准确率 84%，对确认行星的召回率 88%——模型能找出大多数真实行星。

4.4 混淆矩阵#

混淆矩阵可视化预测结果 vs 真实标签：

1
cm = confusion_matrix(y_test, y_pred, labels=[1, 0])
2

3
fig, ax = plt.subplots(figsize=(5, 5))
4

5
disp = ConfusionMatrixDisplay(
6
    confusion_matrix=cm,
7
    display_labels=["confirmed", "false positive"],
8
)
9

10
disp.plot(ax=ax, values_format="d", colorbar=False)
11
plt.title("Confusion matrix — test set")
12
plt.grid(False)
13
plt.show()

左上角（True Positive，366）：正确识别为行星
右下角（True Negative，335）：正确识别为假阳性
右上角（False Negative，51）：行星被误判为假阳性（漏报）
左下角（False Positive，82）：假阳性被误判为行星（误报）

4.5 分析分类错误的案例#

1
test_rows = model_df.loc[test_idx].copy()
2
test_rows["true_label"] = y_test.values
3
test_rows["pred_label"] = y_pred
4
test_rows["confirmed_probability"] = y_proba
5

6
test_rows["correct"] = test_rows["true_label"] == test_rows["pred_label"]
7

8
mistakes = test_rows[~test_rows["correct"]].copy()
9

10
print("Number of test mistakes:", len(mistakes))
11

12
mistakes[[
13
    "kepid",
14
    "kepoi_name",
15
    "kepler_name",
16
    "koi_disposition",
17
    "koi_period",
18
    "koi_depth",
19
    "koi_prad",
20
    "koi_model_snr",
21
    "confirmed_probability",
22
    "true_label",
23
    "pred_label",
24
]].sort_values("confirmed_probability", ascending=False).head(20)

输出（前20条假阳性被误判为行星）：

1
Number of test mistakes: 133
2

3
         kepid kepoi_name kepler_name koi_disposition  koi_period  koi_depth  \
4
2496   5443604  K02713.01         NaN  FALSE POSITIVE   21.391012      645.8
5
2139   8345172  K02385.01         NaN  FALSE POSITIVE   50.571581     1282.6
6
1707   3120276  K01111.01         NaN  FALSE POSITIVE   10.265477      399.6
7
...
8

9
      koi_prad  koi_model_snr  confirmed_probability  true_label  pred_label
10
2496      1.72           25.1               0.834551           0           1
11
2139      2.74           19.9               0.834471           0           1

这些被模型高置信度误判的假阳性，通常具有”看起来像行星”的物理参数：适中的周期、合理的凌星深度和小行星半径。这正是机器学习面临的挑战——有些假阳性在特征空间中与真实行星高度重叠。

4.6 特征重要性#

随机森林可以告诉我们哪些特征对分类贡献最大：

1
importance = pd.DataFrame({
2
    "feature": FEATURES,
3
    "importance": model.feature_importances_,
4
}).sort_values("importance", ascending=True)
5

6
plt.figure(figsize=(8, 4))
7
plt.barh(importance["feature"], importance["importance"])
8
plt.xlabel("Feature importance")
9
plt.title("Which features did the forest use most?")
10
plt.grid(axis="x", alpha=0.3)
11
plt.show()
12

13
importance.sort_values("importance", ascending=False)

通常 log_depth（凌星深度）和 log_prad（行星半径）是最重要的特征——深度越大、半径越大的信号越可能是假阳性（如食双星）。

4.7 过拟合检查#

1
train_pred = model.predict(X_train)
2
test_pred = model.predict(X_test)
3

4
train_acc = accuracy_score(y_train, train_pred)
5
test_acc = accuracy_score(y_test, test_pred)
6

7
print("Train accuracy:", round(train_acc, 3))
8
print("Test accuracy:", round(test_acc, 3))
9

10
if train_acc > test_acc + 0.15:
11
    print("Possible overfitting: train score is much higher than test score.")
12
else:
13
    print("Train/test gap is not extremely large for this demo.")

输出：

1
Train accuracy: 0.867
2
Test accuracy: 0.841
3
Train/test gap is not extremely large for this demo.

训练集（86.7%）与测试集（84.1%）差距仅 2.6 个百分点，模型未严重过拟合。

5. 候选体排序（Candidate Triage）#

5.1 对未分类候选体进行预测#

Kepler 数据中有 806 条 CANDIDATE 状态的记录——它们的真实身份尚未被 NASA 确认。用训练好的模型对它们打分：

1
if len(candidate_df) == 0:
2
    print("No candidate rows available. Skipping candidate triage.")
3
else:
4
    candidate_X = candidate_df[FEATURES]
5
    candidate_df = candidate_df.copy()
6
    candidate_df["confirmed_like_probability"] = model.predict_proba(candidate_X)[:, 1]
7

8
    ranked_candidates = candidate_df.sort_values("confirmed_like_probability", ascending=False)
9

10
    print("Ranked candidate rows:", len(ranked_candidates))
11

12
    display_cols = [
13
        "kepid",
14
        "kepoi_name",
15
        "kepler_name",
16
        "koi_period",
17
        "koi_depth",
18
        "koi_prad",
19
        "koi_model_snr",
20
        "koi_kepmag",
21
        "confirmed_like_probability",
22
    ]
23

24
    display(ranked_candidates[display_cols].head(15))

输出（前 15 个高概率候选体）：

1
Ranked candidate rows: 806
2

3
         kepid kepoi_name kepler_name  koi_period  koi_depth  koi_prad  \
4
3144   4951877  K00501.01         NaN   24.796280      574.4      2.70
5
1561   4242147  K01934.01         NaN   28.782710      864.5      2.11
6
3400   5131180  K00641.01         NaN   14.851855     1341.0      2.73
7
...
8

9
      koi_model_snr  koi_kepmag  confirmed_like_probability
10
3144           43.6      14.612                    0.836956
11
1561           40.1      14.649                    0.836525

模型按概率从高到低排列了所有候选体。这些最有可能的候选体具有：适中的对数深度、小行星半径（1.5−3 地球半径）、高 SNR——与已确认行星的特征高度吻合，值得天文学家优先进行后续观测验证。

6. 本节小结#

本节完成了以下内容：

掌握了 Pandas DataFrame 的核心操作：创建、列筛选、布尔过滤、排序、groupby 分组聚合、新列派生。
构建了特征矩阵（X）和标签向量（y），为监督学习做好了数据准备。
从 NASA Exoplanet Archive 获取了 5000 条真实系外行星候选体数据。
实施了特征工程：对数变换（safe_log10）使天文学数量级数据更适合机器学习模型。
训练了随机森林分类器（RandomForestClassifier），在测试集上达到 84% 准确率和 88% 召回率。
分析了混淆矩阵和特征重要性，理解了模型的优势和局限性。
对 806 个未确认候选体进行了概率排序，实现了自动化候选体筛选。

如果这篇文章对你有帮助，欢迎分享给更多人！

笔记｜天文数据科学03｜机器学习甄别系外行星

https://luq-blog.xyz/posts/2026-07-09-astro-data-science-03-machine-learning-classifier/

作者

Luquiescene

发布于

2026-07-09

许可协议

CC BY-NC-SA 4.0

部分信息可能已经过时

日常｜SCO-YSC日记06｜外出旅行

日常｜SCO-YSC日记05｜逐渐适应中。。。

Luquiesceneの小屋

1. DataFrame 热身练习#

1.1 创建玩具数据集#

1.2 添加新列#

1.3 DataFrame 基础属性#

1.4 列筛选#

1.5 特征矩阵与标签向量#

1.6 布尔条件筛选#

1.7 多条件组合筛选#

1.8 排序#

1.9 值计数与布尔列#

1.10 列运算与分组聚合#

1.11 准备机器学习数据结构#

2. 大规模真实数据#

2.1 环境配置#

2.2 查询 NASA 系外行星数据库#

3. 特征工程#

3.1 对数变换#

3.2 划分训练集#

3.3 类别平衡#

3.4 特征空间可视化#

4. 训练随机森林分类器#

4.1 训练/测试拆分#

4.2 训练模型#

4.3 模型评估#

4.4 混淆矩阵#

4.5 分析分类错误的案例#

4.6 特征重要性#

4.7 过拟合检查#

5. 候选体排序（Candidate Triage）#

5.1 对未分类候选体进行预测#

6. 本节小结#

目录